NEURAL AXON OUTGROWTH MODULATORS

Abstract: Novel classes of neural axon outgrowth promoting and orienting proteins or netrins, nucleic acids encoding netrins and cellular which selectively bind such netrins are disclosed. Agents such as netrin peptides are capable of effecting axon outgrowth, orientation and regeneration. These agents provide small molecular weight modulators of nerve cell growth useful in the treatment of neurological disease and injury. The disclosed compositions also find use variously in screening chemical libraries for regulators of axon outgrowth and orientation, in genetic mapping, as probes for related genes, as diagnostic reagents for genetic neurological disease and in the production of specific cellular and animal systems for the development of neurological disease therapy.

Description: NEURAL AXON OUTGROWTH MODULATORS The research carried out in the subject application was supported in part by grants from the National Institutes of Health. The government may have rights in any patent issuing on this application. INTRODUCTION Technical Field The technical field of this invention concerns proteins involved in spinal axon outgrowth. Background In the developing nervous system, axons project considerable distances along stereotyped pathways to reach their targets. Axon growth and guidance depends partly on the recognition of cell-surface and extracellular matrix cues along these pathways. The identification of such nerve cell growth and guidance cues is the holy grail of neurobiology. These are the compounds that tell neurons when to grow, where to grow, and when to stop growing. The medical applications of such compounds are enormous and include modulating neuronal growth regenerative capacity, treating neurodegenerative disease, and mapping (e.g. diagnosing) genetic neurological defects. Over decades of concentrated research, various hypotheses involving chemo-attractants and repellents, labeled pathways, cell adhesion molecules, etc. have been invoked to explain guidance. Molecules such as N-CAM and N- cadherin have been reported to provide favorable substrates for axon growth and certain sensory axons may be responsive to NGF and NGF-like factors. Recent reports suggest the existence of diffusible chemotropic molecule(s) which influence the pattern and orientation of commissural axon growth. Relevant Literature Placzek et al. (1990) Development 110, 19-30; Placzek et al. (1990) Cold Spring Harbor Symposia on Quantitative Biology 55, 279-302.; and Tessier- Lavigne et al. (1988) Nature 336: 775-778 report evidence for diffusible chemotropic molecules which influence the pattern and orientation of commissural axon growth. Gundersen and Barret (1980) JCB 87, 546-554, Lohof et al. (1992) J. Neurosci. 12 (4), 1253-1261 and Zheng et al. (1993) Soc. Neurosci. Abstr 19, 608.9 report neural chemotaxis in response to NGF, cAMP and acetylcholine, respectively. Ishii et al. (1992) Neuron 9, 873-881 disclose a gene, unc-6, derived from C. elegans, which has sequence similarity to the some of the nucleic acids disclosed herein. For a recent review of axon guidance, see Goodman and Shatz (1993) Cell 72/Neuron 10, 77-98. Much of the data disclosed in this application was published in Serafini et al (1994) Cell 78, 409-424 and Kennedy et al (1994) Cell 78, 425-435 at page 5, column 1. The work was also reported in The New York Times, Section B7, Tuesday, August 16, 1994. SUMMARY OF THE INVENTION Methods and compositions relating to novel classes of neural axon outgrowth promoting and orienting proteins, nucleic acids encoding such proteins and receptors which selectively bind such proteins are disclosed. The disclosed neural axon outgrowth promoting and orienting proteins include p75 (netrin2) and p78 (netrin 1 ) members of the netrin family; the first known family of vertebrate proteins which can promote spinal axon outgrowth in three-dimensions, and netrin- specific receptors, including receptors found on spinal axons, especially growth cones. Also disclosed are agents including peptides derived from the disclosed neural axon outgrowth promoting proteins capable of effecting axon outgrowth, orientation and regeneration. These agents provide small molecular weight modulators of nerve cell growth useful in the treatment of neurological disease and injury. The disclosed compositions also find use variously in screening chemical libraries for regulators of axon outgrowth and orientation, in genetic mapping, as probes for related genes, as diagnostic reagents for genetic neurological disease and in the production of specific cellular and animal systems for the development of neurological disease therapy. SELECTED NUCLEOTTDE AND AMINO ACID SEQUENCES Sequence ID Nos. 1 and 2: Nucleotide and deduced amino acid sequence of chick p78, starting at the initiation methionine. The mature amino-terminus starts at residue 26 (GYP...). Sequence ID Nos. 3 and 4: Nucleotide and deduced amino acid sequence of chick p75, starting inside the signal sequence (the sequence is thought to lack several amino acids from the N-terminus, within the signal sequence). The mature amino terminus starts at residue 16 (ANP...). Sequence ID Nos. 5 and 6: Nucleotide and deduced amino acid sequence of mouse p78. DESCRIPTION OF SPECIFIC EMBODIMENTS The present invention discloses methods and compositions relating to modulators of nerve cell growth and function. The compositions include novel neural axon outgrowth promoting and/or orienting proteins, called netrins and their cellular receptors. These compositions are shown to be capable of selectively promoting neural axon outgrowth and/or orientation. Preferred axon targets are spinal axons - axons residing at least partly in the spinal chords of vertebrates - of interneurons. Furthermore, the many of the compositions of the invention are shown to promote outgrowth in three dimensions in a semi-solid matrix such as a collagen gel or a physiological tissue, as opposed to merely providing a favorable substrate surface. Finally, many of the subject compositions are active as soluble factors. Netrins include a novel class of proteins exemplified by p75 (netrin2) and p78 (netrinl). The invention provides agents, including netrin peptides, which specifically bind and act as agonists for netrin receptors. These agents find a wide variety of clinical, therapeutic and research uses where nerve cell growth is indicated, e.g. traumatic injury to nerve cells, neurodegenerative disease, etc. A wide variety of netrin and netrin receptor-specific binding agents and methods for identifying, making and using the same are described below. The peptides of the invention comprise unique portions of the disclosed netrins and netrin receptors (netrins/receptors). A "unique portion" has an amino acid sequence unique to that disclosed in that it is not found in any previously known protein and has a length at least long enough to define a novel peptide. Unique portions are found to vary from about 5 to about 25 residues, preferably from 5 to 10 residues in length, depending on the particular amino acid sequence and are readily identified by comparing the subject portion sequences with known peptide/protein sequence data bases. Preferred unique portions include netrin residues that directly bind and activate (agonize) netrin receptors, especially residues that derive from the EGF-like domains of the disclosed sequences, especially those of the human varieties. Particular preferred netrin peptides are listed here. These peptides are shown by functional assays disclosed herein to have biological activity including axon outgrowth and/or orienting activity. It is apparent to those of ordinary skill in the art that substitutions of chemically conservative residues can be made while preserving function. Preferred peptides derived from domain V of p75 and p78: 1. NGH AA/SR (SEQ ID NOS.2/4, residues 289-294/265-270) 2. VRD RDD N/SLV (SEQ ID NO:2, residues 296-304) 3. VKD KEQ KLV (SEQ ID NO:4, residues 272-280) 4. KHN TE/AG PE (SEQ ID NOS.2/4, residues 308-315/284-291) 5. KPF HYD RP WQR AT/SA REA NE (SEQ ID NOS.2/4, residues 320- 338/296-314) 6. NLH ARR (SEQ ID NO:2, residues 345-350) 7. RFN MEL YKL SGR KSG GV (SEQ ID NOS.2/4, residues 352-368/328- 344) 8. RHN TAG RH (SEQ ID NOS.2/4, residues 373-380/349-356) 9. KEG FYR DLS KP/SIS/ TH/DR KA (SEQ ID NOS.2/4, residues 385- 401/361-377) 10. HPV GAA GK/QT (SEQ ID NOS:2/4, residues 408-416/384-392) 11. NQT TGQ (SEQ ID NOS.2/4, residues 418-423/394-399) 12. KDG VTG I/LT (SEQ ID NOS.2/4, residues 427-434/403-410) 13. AKG Y/FQQ SRS PI/VA P (SEQ ID NOS.2/4, residues 439-451/415-427) Preferred peptides derived from the C terminal domains of p75 and p78: 14. IKI PAI/AN/P (SEQ ID NOS.2/4, residues 453-459/429-435) 15. IKI PVR (SEQ ID NO:6, residues 377-382) 16. STE A/EPA DCD SYC K (SEQ ID NOS.2/4, residues 466-478/442-454) 17. KI/MN MKK YCK/R KDY V/AVQ (SEQ ID NOS:2/4, residues 485- 499/461-475) 18. KFT I/VNI L/T/ISV YK (SEQ ID NOS.2/4, residues 513-523/489-499) 19. CKC PKI/V (SEQ ID NOS:2/4, residues 545-550/521-526) 20. ADK S/NSL VIQ WRD (SEQ ID NOS.2/4, residues 573-584/549-560) 21. RLR RGD QTL W (SEQ ID NO:2, residues 528-537) 22. RVK RGD NFL W (SEQ ID NO:4, residues 504-513) Preferred peptides derived from domain VI of p75 and p78: 23. DPC YDE (SEQ ID NOS.2/4, residues 40-45/27-32) 24. RCI PE/DF VNA/S AFG KEV (SEQ ID NOS.2/4, residues 51-65/38-52) 25. SST CGK PP (SEQ ID NOS.2/4, residues 68-75/55-62) 26. A/SSD PKR/K AHP PA/S (SEQ ID NO:2, residues 97-107) 27. LTD LNN PH (SEQ ID NO:2, residues 109-116) 28. LTD LNT AA (SEQ ID NO:4, residues 80-87) 29. NL/MT CWR/Q S (SEQ ID NOS.2/4, residues 117-123/88-94) The subject peptides may be free or covalently coupled to other atoms or molecules. Frequently the peptides are present as a portion of a larger polypeptide comprising the subject peptide where the remainder of the polypeptide need not be netrin/receptor-derived. Alternatively, the subject peptide may be present as a portion of a "substantially full-length" netrin/receptor which comprises at least about 200, preferably at least about 300, more preferably at least about 400 amino acids of a disclosed polypeptide sequence. The invention provides polypeptides comprising a sequence substantially similar to that of substantially full-length netrins/receptors. "Substantially similar" sequences share at least about 40%, more preferably at least about 60%, and most preferably at least about 80% sequence identity. Where the sequences diverge, the differences are generally point insertions/deletions or conservative substitutions, i.e. a cysteine/threonine or serine substitution, an acidic/acidic or hydrophobic/hydrophobic amino acid substitution, etc. The subject poly/peptides are "isolated", meaning unaccompanied by at least some of the material with which they are associated in their natural state. Generally, an isolated poly/peptide constitutes at least about 1 % , preferably at least about 10%, and more preferably at least about 50% by weight of the total poly/peptide in a given sample. By pure peptide/polypeptide is intended at least about 60%, preferably at least 80%, and more preferably at least about 90% by weight of total poly/peptide. Included in the subject poly/peptide weight are any atoms, molecules, groups, etc. covalently coupled to the subject poly/peptides, such as detectable labels, glycosylations, phosphorylations, etc. The subject poly/peptides may be isolated or purified in a variety of ways known to those skilled in the art depending on what other components are present in the sample and to what, if anything, the poly/peptide is covalently linked. Purification methods include electrophoretic, molecular, immunological and chromatographic techniques, especially affinity chromatography and RP-HPLC in the case of peptides. For general guidance in suitable purification techniques, see Scopes, R., Protein Purification, Springer- Verlag, NY (1982). The subject poly/peptides generally comprise naturally occurring amino acids but D-amino acids or amino acid mimetics coupled by peptide bonds or peptide bond mimetics may also be used. Amino acid mimetics are other than naturally occurring amino acids that conformationally mimic the amino acid for the purpose of the requisite netrin/receptor binding specificity. Suitable mimetics are known to those of ordinary skill in the art and include β-y-δ amino and imino acids, cyclohexylalanine, adamantylacetic acid, etc., modifications of the amide nitrogen, the α-carbon, amide carbonyl, backbone modifications, etc. See, generally, Morgan and Gainor (1989) Ann. Repts. Med. Chem 24, 243-252; Spatola (1983) Chemistry and Biochemistry of Amino Acids, Peptides and Proteins, Vol VII (Weinstein) and Cho et. al (1993) Science 261, 1303-1305 for the synthesis and screening of oligocarbamates. The subject poly/peptides have netrin/receptor binding specificity meaning that the subject poly/peptide retains a molecular conformation specific to one or more of the disclosed netrins/receptors. As such, binding specificity may be provided by an netrin-specific immunological epitope, lectin binding site, etc. However, preferred netrin binding specificity is specificity for an netrin receptor, and vice versa. "Selective binding" is empirically determined by contacting, for example a netrin receptor poly/peptide with a mixture of components and identifying those components that preferentially bind the peptide. Selective binding is most conveniently shown by competition with labeled ligand using recombinant netrin peptide either in vitro or in cellular expression systems as disclosed herein. Generally, selective binding requires a binding affinity of lO^M, preferably 10 "8 M, more preferably 10 "10 M, under in vitro conditions as exemplified below. The poly/peptides may be modified or joined to other compounds using physical, chemical, and molecular techniques disclosed or cited herein or otherwise known to those skilled in the relevant art to affect their netrin/receptor binding specificity or other properties such as solubility, membrane transportability, stability, toxicity, bioavailability, localization, detectability, in vivo half-life, etc. as assayed by methods disclosed herein or otherwise known to those of ordinary skill in the art. For example, point mutations are introduced by site directed mutagenesis of nucleotides in the DNA encoding the disclosed poly/peptides or in the course of in vitro peptide synthesis. Other modifications to further modulate binding specificity/affinity include chemical/enzymatic intervention (e.g. fatty acid-acylation, proteolysis, glycosylation) and especially where the poly/peptide is integrated into a larger polypeptide, selection of a particular expression host, etc. Amino and/or carboxyl termini may be functionalized e.g., for the ammo group, acylation or alkylation, and for the carboxyl group, esterification or amidification, or the like. Many of the disclosed poly/peptides contain glycosylation sites and patterns which may be disrupted or modified, e.g. by enzymes like glycosidases. For instance, N or O-linked glycosylation sites of the disclosed poly/peptides may be deleted or substituted for by another basic amino acid such as Lys or His for N- linked glycosylation alterations, or deletions or polar substitutions are introduced at Ser and Thr residues for modulating O-linked glycosylation. Glycosylation variants are also produced by selecting appropriate host cells, e.g. yeast, insect, or various mammalian cells, or by in vitro methods such as neuraminidase digestion. Other covalent modifications of the disclosed poly/peptides may be introduced by reacting the targeted amino acid residues with an organic derivatizing (e.g. methyl- 3-[(p-azido-phenyl)dithio] propioimidate) or crosslinking agent (e.g. 1,1- bis(diazoacetyl)-2-phenylethane) capable of reacting with selected side chains or termini. For therapeutic and diagnostic localization, the subject poly/peptides thereof may be labeled directly (radioisotopes, fluorescers, etc.) or indirectly with an agent capable of providing a detectable signal, for example, a heart muscle kinase labeling site. Using the disclosed netrin poly/peptides, netrin receptors are identified by a variety of techniques known to those skilled in the art where a ligand to the target receptor is known, including expression cloning. For other examples of receptor isolation with known ligand using expression cloning, see, Staunton et al (1989) Nature 339, 61; Davis et al (1991) Science 253, 59; Lin et al (1992) Cell 68, 775; Gearing et al (1989) EMBO 8, 3667; Aruffo and Seed (1987) PNAS 84, 8573 and references therein. Generally, COS cells are transfected to express a fetal brain cDNA library or PCR product and cells producing poly/peptides which bind a target netrin poly/peptide are isolated. Alternatively, PCR primers based upon sequences disclosed herein are used to amplify PCR product from such tissues/cells. Other receptor/ligand isolation methods using immobilized ligand or antibody are known to those skilled in the art. Additional netrin peptides with receptor binding specificity are identified by a variety of ways including crosslinking to receptor or specific antibody, or preferably, by screening such peptides for binding or disruption of netrin-netrin receptor binding. For example, netrin mutants, including deletion mutants are generated from and used to identify regions important for specific protein-ligand or protein-protein interactions, for example, by assaying for the ability to mediate axon outgrowth in cell-based assays as described herein. Further, structural x-ray crystallographic and/or NMR data of the disclosed protein are used to rationally design binding molecules of determined structure or complementarity for modulating axon outgrowth and guidance. Additional netrin/receptor-specific agents include specific antibodies that can be modified to a monovalent form, such as Fab, Fab', or Fv, specifically binding oligopeptides or oligonucleotides and most preferably, small molecular weight organic receptor agonists. For example, the disclosed netrin and netrin receptor peptides are used as immunogens to generate specific polyclonal or monoclonal antibodies. See, Harlow and Lane (1988) Antibodies, A Laboratory Manual, Cold Spring Harbor Laboratory, for general methods. Anti-idiotypic antibody, especially internal imaging anti-ids are also prepared using the disclosures herein. Other prospective netrin/receptor specific agents are screened from large libraries of synthetic or natural compounds. For example, numerous means are available for random and directed synthesis of saccharide, peptide, and nucleic acid based compounds. Alternatively, libraries of natural compounds in the form of bacterial, fungal, plant and animal extracts are available or readily producible. Additionally, natural and synthetically produced libraries and compounds are readily modified through conventional chemical, physical, and biochemical means. See, e.g. Houghten et al. and Lam et al (1991) Nature 354, 84 and 81, respectively and Blake and Litzi-Davis (1992), Bioconjugate Chem 3, 510. Useful agents are identified with assays employing a compound comprising the subject poly/peptides or encoding nucleic acids. A wide variety of in vitro, cell-free binding assays, especially assays for specific binding to immobilized compounds comprising netrin/receptor poly/peptide find convenient use. See, e.g. Fodor et al (1991) Science 251, 767 for the light directed parallel synthesis method. Such assays are amenable to scale-up, high throughput usage suitable for volume drug screening. While less preferred, cell-based assays may be used to determine specific effects of prospective agents on e.g. netrin receptor function. Useful agents are typically those that bind to and activate an netrin receptor, e.g. induce axon outgrowth and/or orientation. Preferred agents are receptor- specific and do not cross react with other neural or lymphoid cell membrane proteins. Useful agents may be found within numerous chemical classes, though typically they are organic compounds; preferably small organic compounds. Small organic compounds have a molecular weight of more than 150 yet less than about 4,500, preferably less than about 1500, more preferably, less than about 500. Exemplary classes include peptides, saccharides, steroids, heterocyclics, polycyclics, substituted aromatic compounds, and the like. Selected agents may be modified to enhance efficacy, stability, pharmaceutical compatibility, and the like. Structural identification of an agent may be used to identify, generate, or screen additional agents. For example, where peptide agents are identified, they may be modified in a variety of ways as described above, e.g.to enhance their proteolytic stability. Other methods of stabilization may include encapsulation, for example, in liposomes, etc. The subject binding agents are prepared in any convenient way known to those skilled in the art. For therapeutic uses, the compositions and agents disclosed herein may be administered by any convenient way. Small organics are preferably administered orally; other compositions and agents are preferably administered parenterally, conveniently in a pharmaceutically or physiologically acceptable carrier, e.g., phosphate buffered saline, or the like. Typically, the compositions are added to a retained physiological fluid such as blood or synovial fluid. For CNS administration, a variety of techniques are available for promoting transfer of the therapeutic across the blood brain barrier including disruption by surgery or injection, drugs which transiently open adhesion contact between CNS vasculature endothelial cells, and compounds which facilitate translocation through such cells. As examples, many of the disclosed therapeutics are amenable to direct injection or infusion, topical, intratracheal/nasal administration e.g. through aerosal, intraocularly, or within/on implants e.g. fibers e.g. collagen, osmotic pumps, grafts comprising appropriately transformed cells, etc. A particularly useful application involves coating, imbedding or derivatizing fibers, such as collagen fibers, protein polymers, etc. with therapuetic peptides. Other useful approaches are described in Otto et al. (1989) J Neuroscience Research 22, 83-91 and Otto and Unsicker (1990) J Neuroscience 10, 1912-1921. Generally, the amount administered will be empirically determined, typically in the range of about 10 to 1000 μg/kg of the recipient. For peptide agents, the concentration will generally be in the range of about 50 to 500 μg/ml in the dose administered. Other additives may be included, such as stabilizers, bactericides, etc. These additives will be present in conventional amounts. The invention provides isolated nucleic acids encoding the disclosed poly/peptides. An "isolated" nucleic acid is present as other than a naturally occurring chromosome or transcript in its natural state and is typically joined in sequence to at least one nucleotide with which it is not normally associated on a natural chromosome. Nucleic acids with substantial sequence similarity hybridize under low stringency conditions, for example, at 50°C and SSC (0.9 M saline/0.09 M sodium citrate) and remain bound when subject to washing at 55 °C with SSC. Regions of non-identity of substantially similar nucleic acid sequences preferably encode redundant codons. A partially pure nucleotide sequence constitutes at least about 5%, preferably at least about 30%, and more preferably at least about 90% by weight of total nucleic acid present in a given fraction. Unique portions of the disclosed nucleic acids are of length sufficient to distinguish previously known nucleic acids. Thus, a unique portion has a nucleotide sequence at least long enough to define a novel oligonucleotide, usually at least about 18 bp in length. The invention also provides for the disclosed nucleic acids modified by transitions, transversions, deletions, insertions, or other modifications such as alternative splicing and also provides for genomic sequences, and gene flanking sequences, including regulatory sequences; included are DNA and RNA sequences, sense and antisense. Preferred DNA sequence portions encode the preferred amino acid sequence portions disclosed above. For antisense applications where the inhibition of expression is indicated, especially useful oligonucleotides are between about 10 and 30 nucleotides in length and include sequences surrounding the disclosed ATG start site, especially the oligonucleotides defined by the disclosed sequence beginning about 5 nucleotides before the start site and ending about 10 nucleotides after the disclosed start site. Typically, the invention's netrin/receptor poly/peptide encoding polynucleotides are associated with heterologous sequences. Examples of such heterologous sequences include regulatory sequences such as promoters, enhancers, response elements, signal sequences, polyadenylation sequences, etc., introns, 5' and 3' noncoding regions, etc. According to a particular embodiment of the invention, portions of the coding sequence are spliced with heterologous sequences to produce soluble, secreted fusion proteins, using appropriate signal sequences and optionally, a fusion partner such as /3-Gal. The netrin/receptor encoding nucleic acids can be subject to altemative purification, synthesis, modification, sequencing, expression, transfection, administration or other use by methods disclosed in standard manuals such as Molecular Cloning, A Laboratory Manual (2nd Ed., Sambrook, Fritsch and Maniatis, Cold Spring Harbor), Current Protocols in Molecular Biology (Eds. Aufubel, Brent, Kingston, More, Feidman, Smith and Stuhl, Greene Publ. Assoc., Wiley-Interscience, NY, NY, 1992) or that are otherwise known in the art. The invention also provides vectors comprising nucleic acids encoding netrin/receptor poly/peptides. A large number of vectors, including plasmid and viral vectors, have been described for expression in a variety of eukaryotic and prokaryotic hosts. Advantageously, vectors will often include a promotor operably linked to the netrin/receptor poly/peptide-encoding portion, one or more replication systems for cloning or expression, one or more markers for selection in the host, e.g. antibiotic resistance. The inserted coding sequences may be synthesized, isolated from natural sources, prepared as hybrids, etc. Suitable host cells may be transformed/transfected/infected by any suitable method including electroporation, CaClj mediated DNA uptake, viral infection, microinjection, microprojectile, or other methods. Appropriate host cells include bacteria, archebacteria, fungi, especially yeast, and plant and animal cells, especially mammalian cells. Of particular interest are E. coli. B. subtilis. Saccharomyces cerevisiae. SF9 cells, C129 cells, 293 cells, Neurospora, and CHO, COS, HeLa cells, immortalized mammalian myeloid and lymphoid cell lines, and pluripotent cells, especially mammalian ES cells and zygotes. Preferred expression systems include COS-7, 293, BHK, CHO, TM4, CVl, VERO-76, HELA, MDCK, BRL 3A, W138, Hep G2, MMT 060562, TRI cells, and baculovirus systems. Preferred replication systems include M13, ColEl, SV40, baculovirus, lambda, adenovirus, AAV, BPV, etc. A large number of transcription initiation and termination regulatory regions have been isolated and shown to be effective in the transcription and translation of heterologous proteins in the various hosts. Examples of these regions, methods of isolation, manner of manipulation, etc. are known in the art. For the production of stably transformed cells and transgenic animals, the subject nucleic acids may be integrated into a host genome by recombination events. For example, such a nucleic acid can be electroporated into a cell, and thereby effect homologous recombination at the site of an endogenous gene, an analog or pseudogene thereof, or a sequence with substantial identity to an netrin/receptor-encoding gene. Other recombination-based methods such as nonhomologous recombinations, deletion of endogenous gene by homologous recombination, especially in pluripotent cells, etc. , provide additional applications. Preferred transgenics and stable transformants over-express or under-express (e.g. knock-out cells and animals) a disclosed netrin/receptor gene and find use in drug development and as a disease model. Methods for making transgenic animals, usually rodents, from ES cells or zygotes are known to those skilled in the art. The compositions and methods disclosed herein may be used to effect gene therapy. See, e.g. Zhu et al. (1993) Science 261, 209-211; Gutierrez et al. (1992) Lancet 339, 715-721. For example, cells are transfected with netrin/receptor- encoding sequences operably linked to gene regulatory sequences capable of effecting altered netrin/receptor expression or regulation. To modulate netrin/receptor translation, target cells may be transfected with complementary antisense polynucleotides. For gene therapy involving the grafting/implanting/transfusion of transfected cells, administration will depend on a number of variables that are ascertained empirically. For example, the number of cells will vary depending on the stability of the transfered cells. Transfer media is typically a buffered saline solution or other pharmacologically acceptable solution. Similarly the amount of other administered compositions, e.g. transfected nucleic acid, protein, etc., will depend on the manner of administration, purpose of the therapy, and the like. The following examples are offered by way of illustration and not by way of limitation. EXAMPLES 1. Development of a novel assay for commissural axon outgrowth In our published work, the outgrowth-promoting activity of floor plate cells was assayed on Ell rat dorsal spinal cord. In these experiments, two-segment stretches of El 1 dorsal spinal cord are cocultured with floor plate in collagen gels for 40 hr (Tessier-Lavigne et al, 1988). In initial attempts to screen potentially more abundant tissue sources for activity, we found that this assay is very sensitive to impurities present in crude tissue homogenates, so that it was necessary to identify a more robust assay. We therefore tested whether the floor plate could also promote the outgrowth of commissural axons from older spinal cord, which was expected to be less fragile. When small pieces of dorsal spinal cord (approximately 50 μ X 50 μm) were cultured with floor plate in collagen gels, dramatic outgrowth of axons was observed after 16hr of culture; at that time, little or no outgrowth was observed in cultures without floor plate. Floor plate- conditioned medium had the same effect as floor plate tissue; moreover, when conditioned medium was titered, it was found that it was as effective in promoting outgrowth from El 3 explants as from El l explants. The E13 tissue was found to be more robust than the Ell tissue; i.e., it was not killed by crude extracts. It was therefore used to screen for a more abundant source of activity and to purify the activity. 2. Identification of embryonic brain as a source of commissural axon outgrowth- promoting activity Floor plate tissue is too small a source of commissural axon outgrowth- promoting activity to effect a purification. To try to identify a more abundant source of activity, we screened a number of adult and embryonic tissues. Because we were concerned that activity might be present at too low a level to be detected, we first sought to identify a few steps of purification and enrichment of the activity in floor plate homogenates, with the aim of applying these steps to potentially more abundant sources. When floor plate homogenates were applied to dorsal spinal cord explants, robust commissural axon outgrowth was evoked by these homogenates. When the homogenates were fractionated into soluble and membrane fractions, essentially all the activity was found associated with the membranes. We found that the activity in floor plate membranes could be solubilized by exposure to 1 M NaCl. We therefore screened several tissues for the presence of commissural axon outgrowth activity by making tissue homogenates, isolating a membrane fraction, and extracting this fraction with 1 M NaCl. This showed that embryonic brain contained commissural axon outgrowth activity. Activity was detected in both rat and chick brain, but the latter was used for further characterization and purification due to the relative ease with which it can be isolated. 3. Molecular dissection of the activity in embryonic brain We analyzed whole chick embryos (E4 through E7) and dissected brains (E10 and E13) as to relative ease of dissection and ability to accumulate large amounts of source material, through the isolation of membrane fractions with subsequent 1 M NaCl extraction and E13 assay. We found that E10 brain was roughly equivalent to E7 whole embryo in terms of the speed with which we could accumulate total activity; however, because we expected the protein composition of brain tissue to be less complex, we decided to use this tissue as the source material for our purification. Likewise, although homogenization of embryonic brain tissue using either a Potter-Ehrehjem homogenizer or Waring blender led to equal recoveries of the activity, the specific activity in salt extracts was higher in the former, and thus the gentler method of homogenization was used. Differential centrifugation experiments identified the microsomal membrane fraction as containing almost all of the salt-extractable activity. Although this differential centrifugation strategy leads to only modest increases in specific activity, we nonetheless retained these steps at the onset of the purification scheme because we expected to decrease the complexity of the eventual salt extract by increasing the homogeneity of the membrane fraction. Differential salt extraction of microsomal membrane fractions led to a large increase in specific activity. Therefore, a low salt wash at approximatley 500 mM NaCl followed by a high salt extraction of the activity at approximately 1 M NaCl was routinely used to prepare a soluble form of the activity amenable to column chromatography. The first chromatography step (Heparin Sepharose CL-6B) served both to purify and to concentrate the activity. In order to maximize the purification, the column was loaded at approximately 0.9 M NaCl, a salt concetration at which the activity partitioned into the stationary phase just enough to prevent bleed-through during loading and washing. The 2 M NaCl eluate from the column contained all of the outgrowth promoting activity present in the column fractions. In addition, however, we discovered that the flow-through fraction, containing the bulk of the protein, contained an activity which synergizes with eluted activity. At low concentrations of the eluate (which we term the " " Fraction), the flow-through fraction (the "β" Fraction) acted to enhance the outgrowth (in terms of fascicle length, number, and thickness) of commissural axons elicited by the former. At higher concentrations of or the effect of β is less pronounced. The β Fraction by itself caused no outgrowth in these experiments. In order to maximize the sensitivity of the assay to the active component in the a Fraction, β was routinely included in the assays of fractions generated at this step of the purification and beyond. We term the activity in the β Fraction which synergizes with the Fraction "SA" (for "synergizing activity"). In subsequent experiments, SA was shown to be stable to boiling and freeze/ thawing, retained by 10K MW cut-off filters, and protease sensitive. Purification, characterization and gene cloning of β are performed analogously to that of a. Three subsequent steps of purification follow: Wheat Germ Agglutinin (WGA) Agarose, Heparin Sepharose High Performance (HSHP), and Immobilized Metal Adsorption Chromatography (IMAC) on a Zn 2+ -charged resin. At this last step, outgrowth-promoting activity was found to co-chromatograph separately with two proteins: one of 75 kD (as assessed by SDS-PAGE) which eluted isocratically from the column at approximately a pH of 6.5, and one of 78 kD which eluted during the application of a decreasing pH gradient at a pH of approximately 6.1. As judged by silver staining of overloaded SDS-PAGE gels of the active fractions, the two proteins have been purified to homogeneity. (A faint band of slightly lower molecular weight is present in the fractions containing p75, in exactly the same relative abundance as p75, indicative of a differentially glycosylated form of the protein.) For SDS-PAGE and activity profile of IMAC fractions (final step in purification), two hundred μl of each fraction from the IMAC chromatography step of the purification of p75 and p78 was TCA precipitated and subjected to SDS- PAGE and silver staining. p75 was seen to elute in fractions 4-8, while p78 eluted in fractions 10-16; the activity profile mirrors the presence of the two proteins in the fractions. To develop the purification of p75 and p78, approximately 20,000 E10 chick brains were used. From 2000 E10 chick brains (one purification run), approximately 10 μg p78 and 3 μg p75 can be obtained after an approximate 30,000-fold purification with an approximately 2% yield. 4. Requirement for both p75 / p78 and SA for reconstitution of floor plate effect on El 1 explants Surprisingly, whereas p75 and p78, when added to the medium of El 3 explant cultures, were both equally capable of evoking the full response seen when these E13 explants are cocultured with floor plate, the proteins were relatively incapable of causing this robust outgrowth from El 1 explants. However, with the addition of SA (i.e., the β Fraction), the full effect was reconstituted. Because only one unit of each of the two fractions suffices to elicit this response, while double that amount of each separately has almost no effect, one can conclude that the two activities are synergistic rather than additive. Two units of either a mix of p75 and p78 or SA alone have little or no effect on an El 1 dorsal explant (compare with control), yet culturing such an explant with only one unit of p75 / p78 and only one unit of SA leads to robust outgrowth. 5. Protein sequencing of p75 and p78 Purified p75 and p78 from approximately 5000 E10 chick brains (two and one-half purification runs) was trichloroacetic acid (TCA) precipitated and cleaved with cyanogen bromide (CNBr). The resulting peptides were separated by SDS- PAGE and electroblotted to polyvinylidene difluoride (PVDF) membrane, from which they were subjected to gas phase Edman degradation sequencing directly. In addition, purified protein was sequenced directly in order to obtain N-terminal sequence. The resultant sequences suggested that at least portions of the two proteins were very homologous, since sequence (1) from p78 and sequence (1) from p75 were identical. However, the sequences also showed that p75 and p78 are distinct proteins, since sequence (3) from p78 and sequence (2) from p75 are homologous but distinct. 6. RNA isolation Total RNA was isolated from E10 chick brains as described (Auffray and Rougeon, 1980). 7. PCR amplification of fragments of the cDNAs for p75 and p78 p78: Degenerate oligonucleotide primers were made based upon the amino acid sequences obtained for p78 peptides. These primers represented the sequences both in sense and antisense orientations, as the placement of the sequences relative to one another in the full sequence of the protein was unknown. Because PCR using pairs of these primers yielded very heterogeneous mixtures of products, a nested PCR strategy was employed. In this strategy, primers (presumably) internal to those used in primary reactions are used in secondary PCR in order to selectively amplify bona fide fragments of the cDNA of interest from the mixture of primary reaction products. Using such a strategy, three primers were used to amplify a single 92 bp fragment. Because the sequence of this fragment was found to encode p78 peptide sequence not used for any of the three primers (and found in correct orientation with respect to the primers), this PCR product was a fragment of the cDNA for p78, yielding 62 bp of unique, nondegenerate sequence for the cDNA. p75: A nested PCR strategy was also used to amplify a fragment of the cDNA encoding p75. Because an alignment of the derived p78 amino acid sequence showed that regions of identity existed between p78 and the B2 chains of laminin (see Sequences, below), and the peptide sequences obtained for p75 suggested that p75 and p78 were very homologous, it was very likely that those regions of identity between p78 and the laminin B2 chains would also be conserved in p75. Furthermore, the alignment allowed a prediction of the relative placement of p75 peptide sequences relative to one another. Therefore, a primer for the second stage of the nested PCR was designed based upon sequences within p78 that were identical to sequences of the laminin B2 chains and were predicted to lie within the amplified fragment generated using the selected first stage PCR primers. Also, the alignment of p78 and laminin B2 sequences allowed sense and antisense primers to be selected in accordance with their expected positions relative to one another. After performing the nested PCR, restriction digestion of the "single" amplified product eliminated any p78 sequences from the DNA that was subsequently cloned and sequenced. Sequencing of a 377 bp fragment resulting from the PCR and subsequent digestion yielded a derived amino acid sequence that was highly homologous to that of p78; therefore, this fragment was very likely to be a fragment of the gene for p75, which was borne out after the entire cDNA was cloned and sequenced, and the N-terminal sequence obtained for p75 was present at the predicted N-terminus of the mature protein (see below). 8. Library construction and screening In order to isolate cDNAs corresponding to p78 and p75 an E10 chick brain cDNA library was constructed. A 61 bp a 32 P-dCTP labelled probe to p78 was generated by PCR using primers complementary to the original p78 fragment sequence described above. A 258 bp probe was also generated for p75 by PCR. Using these probes, and probes generated from additional p75 and p78 clones as the screening proceeded, a total of 3 X IO 6 clones of the E10 chick brain cDNA library were screened yielding two partial p78 clones and eleven partial p75 clones. An additional partial p78 clone was identified in a screen of 2 X IO 6 clones from an amplified E2.5 chick spinal cord library. 9. 3' RACE and specifically primed cDNA libraries Following these screens, cDNAs containing 5' coding sequence of p75 and 3' coding sequence of p78 had not been obtained. A 3' RACE protocol was used to obtain the 3' coding sequence of p78 (as described by Frohman and Martin, 1989). The sequence obtained using 3' RACE was used to design a p78 oligonucleotide complementary to sequence 3' of the translational stop codon, which was then used to prime the synthesis of first strand cDNA for the generation of a library enriched in p78 sequences. Similarly, sequence 3' to the translational stop site in one of the p75 cDNAs and sequence at the 5' end of one of the partial p75 cDNA clones were used to generate two primers to prime the first strand synthesis of cDNA libraries designed to obtain the missing 5' sequence of p75. cDNA synthesized in this way was cloned directly into pBluescript (Stratagene). Screens of these plasmid libraries using probes derived from the partial p75 and p78 cDNAs were used to identify cDNAs containing the full coding sequences of p75 and p78. 10. Northern and Southern analysis, and in situ hybridization Northern analysis suggested that p78 and p75 are each encoded in E10 chick brain by approximately 4 kb transcripts and Southern analysis confirmed that p78 and p75 are each encoded by different genes. In situ hybridization to E2.5 chick embryo sections and whole mounts revealed that p78 is expressed in the floor plate of the spinal cord, consistent with it contributing to the chemoattractant and outgrowth promoting properties of the floor plate. p75 transcripts were found in an apparent ventral to dorsal gradient within the spinal cord, implicating a role for it, too, in axon guidance within the developing spinal cord. These functions of p75 and p78 are confirmed using function blocking antibodies generated against recombinant p75 and p78. 11. Expressed recombinant p75 and p78 Recombinant p75 and p78 are obtained from culture supematants and cell extracts of COS cells transfected with SV40-origin containing expression vectors. Large amounts of p75 and p78 are also obtained from recombinant baculovirus infected Sf9 cells. 12. Sequences The derived amino acid sequences for chick p75 and p78 are shown in Sequence ID No: 2 and 4. Their structures indicate secreted proteins: Each has an amino-terminal signal sequence (von Heijne, 1983), followed immediately by a mature amino-terminal sequence that is identical to the peptide sequence obtained by microsequencing; there is no other hydrophobic stretch that could represent a transmembrane domain in either protein, nor does either have any indication at its C-terminus of a potential phospholipid linkage. The deduced sizes of the mature proteins are 580 and 566 amino acids for p78 and p75, respectively. There is a very high degree of amino acid sequence homology between the two proteins: 69% identity over the entire coding region, and even more so in the amino terminal two-thirds of the proteins (see below). Further analysis of the protein sequences shows that each protein is divided into three structural domains with distinct functional roles. The amino terminal two thirds of the proteins are homologous in amino acid sequence to the amino termini of the B chains of laminin, a large heterotrimeric glycoprotein of the extracellular matrix (its three chains are called A, Bl and B2). This region of homology corresponds to two domains termed VI and V of the laminin chains. Because of this homology, we will also term these regions of p75 and p78 domains VI and V. The remaining C terminal thirds of p75 and p78 are homologous to each other, but diverge completely from the laminin sequence. Each domain is briefly discussed in turn, starting with the middle one. Domain V: The amino acid sequences of p75 and p78 are almost identical in this region (Sequence ID No 2: residues 285-453; Sequence ID No 4: residues 261-429; 90% identity over 168 amino acids). The sequences are rich in cysteine residues, which are arranged in a pattern characteristic of so-called EGF-like repeats (Engel, 1989). p75 and p78 each have three EGF-like repeats that make up domain V. The pattern of disulfide linkages in these repeats can be inferred from what is known of the structure of EGF-like repeats (Engel, 1989). The disulfide likages between cysteine residues are oriented to confer a rod-like rigid structure on this region of the polypeptide; loops of amino acids protrude from this backbone, and are available for interaction with other proteins and macromolecules. As in other proteins (Engel, 1989), the loop regions of EGF-like repeats in p75 and p78 are shown to play important roles in cell signaling and adhesions. For example, loop regions are functionally expressed with signal sequences and assayed singly or in combination with other regions, for activity on nerve cells (See, Mayer et al., (1993) EMBO J 125, 1879-1885). Further, residues within the loops are sequentially mutated by insertion, deletion or substitution to identify loops with enhanced or modified activities. Accordingly, peptides comprising p75 and p78-derived EGF-like repeat sequences providing a wide variety of specific neuomodulating activities are provided. Domain VI: This domain in p75 and p78 (Sequence ID No 2: residues 26 to 284; Sequence ID No 4: residues 16 to 260) also shows several regions of amino acid sequence homology with domain VI of laminin B chains, in particular with B2 chains of several species. In laminin, domain VI is thought to mediate a calcium dependent assembly of laminin polymers (Yurchenco and Cheng, 1993). In p75 and p78, regions within domain VI are similarly shown to be involved in protein-protein complex formation. Domain VI eptides are functionally expressed with signal sequences and assayed singly or in combination with other regions, for activity on nerve cells (See, supra). C terminal third: The C-terminal third of p75 and p78 (Sequence ID No 2: resiudes 454 to 605; Sequence ID No 4: residues 430 to 581) is unrelated to laminin sequences. There is a small degree of homology to the C-terminal regions of complement components C3, C4 and C5. In p75 and p78, the C terminal third is rich in basic residues (lysine (K) and arginine (R)), which may explain the tight binding of these proteins to heparin. These regions might therefore also bind heparan-sulfate and mediate binding of p75 and p78 to heparan-sulfate proteoglycans on the surface of the neural cells; this could serve to modulate the functions of these proteins, as binding to heparan-sulfate proteoglycans is known to modulate the function of aFGF (Massague, 1991). This domain also contains the amino acid sequence RGD which is shown to mediate cell attachment and guidance. C terminal regions are functionally expressed with signal sequences and assayed singly or in combination with other regions, for activity on nerve cells (See, supra). 13. Mammalian homologues of p75 and p78 The identification of the amino acid sequences of p75 and p78 and the demonstration of regions of homology between the proteins shows that they define a novel family of proteins that are distantly related to the laminin family of extracellular glycoproteins. The differences in sequence between p75 / p78 and laminins are sufficient to enable the cloning of cDNAs for the homologues of these genes in other species. We used the chick p75 and p78 sequences to identify conserved amino acid sequences, which were then used to design degenerate oligonucleotide primers for the amplification of a fragment of the mouse p78 cDNA (Sequence ID No. 5). This cDNA fragment has been used to isolate the entire coding sequence of mouse p78 (Sequence ID No. 6). This strategy, together with low stringency hybridization screening of genomic and cDNA libraries, is used to isolate p75 from mouse, and p75 and p78 sequences from human. 14. Other members of the p75/p78 family The disclosed p75 and p78 sequences enable the identification of other members of this novel p75/p78 family of proteins. First, degenerate oligonucleotide primers for PCR amplification of fragments of cDNAs or genomic DNA encoding other family members in various species are designed. p75 and p78 sequences isolated from several species (e.g. chick, mouse and human) are aligned to show which residues are most conserved. Preferred primers are derived from highly conserved residues in the C-terminal third of the proteins, where they diverge most from other proteins (in particular laminin). These oligonucleotides are also used directly to screen libraries at high stringency. Second, cDNA and genomic libraries are screened by low-stingency hybridization using fragments of p75 or p78. Regions of the genes that are most homologous to one another but most divergent from other genes in the database provide the best probes for this purpose. Mutagenesis studies have suggested that a gene called unc-6 gene is necessary for the guidance of pioneer axons and migrating cells along the body wall in C. elegans. The putative translation product of this gene has never been characterized nor has its function been clarified. The present invention discloses the translation product of unc-6 to be another member of the p75/p78 family with analogous structural and functional properties. Functions of proteins of the p75/78 family. p75 and p78 were identified on the basis of their ability to promote commissural axon outgrowth into collagen gels. However, these proteins are shown to have other functions, as well as actions on different classes of neurons and non-neuronal cells. First, the proteins are shown to promote outgrowth in a variey of other matrices, not just collagen. Collagen is in fact a very unfavorable environment for the growth of commissural axons (these axons normally never encounter collagen in a normal organism). The ability of the proteins to promote outgrowth into this unfavorable environment suggested that the proteins could also promote outgrowth of these axons into other enviroments, such as glial scars in the adult nervous system or other components of the adult spinal cord and assist in the stimulation of spinal axon growth following trauma to the spinal cord. Second, p75 and p78 were isolated on the basis of their ability to mimic one of the functions of the floor plate (outgrowth promotion). The floor plate also has another important function, namely the ability to orient commissural axon growth (i.e. , chemoattraction: Tessier-Lavigne et al, 1988; Placzek et al, 1990a). In previous experiments, we showed that commissural axon orientation activity was found not just in the floor plate but also to a lesser extent in the ventral spinal cord and dermomyotome (Placzek et al, 1990b). The isolation of p75 and p78 reported here enabled us to examine their sites of expression in the embryo and demonstrate restricted distributions that correspond to the previously defined sites of orientation activity: p78 is expressed in floor plate, p75 in ventral spinal cord, and both p75 and p78 are expressed in dermomyotome. Orientation activity is assayed by expressing p75 and p78 and peptides therefrom in COS cells (see Methods) and testing the ability of the COS cells to orient axon growth in the assay we have previously described (Placzek et al, 1990a). In this way, p75/p78 peptides with specified axon promoting and/or orienting activity are identified. Third, the proteins have functions other than outgrowth promotion and orientation of axons. As discussed in the previous section, the highly basic C- terminal domain in the two proteins can function as a heparin-binding domain, capable of mediating substrate adhesion of neural and non-neural cells via heparan- sulfate proteoglycans on their surfaces. This is assayed by showing substrate adsorbed p75 and p78 mediation of cell adhesion, and inhibition by heparin. The proteins also have growth factor-like or trophic effects (i.e., effects on the proliferation, survival, and health of neural and non-neural cells). In fact, laminin itself has mitogenic and trophic effects, in addition to its ability to stimulate cell adhesion and motility (Kleinman et al, 1993). Many molecules that have adhesive properties for some cells have also been shown to have anti-adhesive and growth inhibiting properties for other cells (Calof and Lander, 1991); such functions are further characterized in standard assays using recombinant p75 and p78. Fourth, p75 and p78 have effects on cells other than the commissural neurons that were used to assay their presence during purification. Northern and in situ hybridization analysis shows that p75 and p78 are expressed in brain regions where commissural axons are absent and we have found them to be expressed outside of the nervous system. There are several other examples of molecules affecting the migration of neural cells that also affect non-neuronal cells, in some cases playing a role in tumor cell migration and metastasis (Kleinman, 1993). METHODS: Tissue culture Assays using embryonic day 11 (Ell; EO = day of vaginal plug) rat dorsal spinal cord were performed as described (Tessier-Lavigne et al., 1988). For E13 assays, spinal cords were isolated from E13 embryos by dissection in L15 medium (Gibco), opened at the roof plate, and flattened down on the dissection dish in an "open book" configuration (Bovolenta and Dodd, 1990). Electrolytically sharpened tungsten needles were used to dissect approximately 50 μm X 50 μm square pieces of dorsal spinal cord in L15 containing 5% heat-inactivated horse serum (HIHS). These dorsal spinal cord explants were embedded in collagen gels as described (Tessier-Lavigne et al., 1988), with four explants in each gel, with or without floor plate. Once the collagen had set, complete medium containing 5 % HIHS (Tessier-Lavigne et al, 1988) was added to the wells, and explants were cultured in a humidified incubator in the presence of 5% CO 2 . Analysis of floor plate homogenates Floor plates were dissected from El 3 rat spinal cords and kept in L15 on ice. Homogenates were prepared exactly as described by Walter et al (1987), using approximately 1 ml of homogenization buffer per 40 floor plates. After a low speed spin to pellet nuclei and cell debris (1000 X g, 10 min, 4 * C), the homogenate was spun at high speed (100,000 X g, 1 hr, 4 * C). The supernatant was dialyzed against L15 salts (Gibco) and assayed. The pellet was resuspended in 1 M NaCl with protease inhibitors (Walter et al., 1987), incubated for 1 hr at 4 °C, and spun again at high speed. The supernatant was dialyzed against L15 salts and assayed. Analysis of embryonic chick brain activity E4, E5, E6, and E7 embryos, and E13 embryonic brains were homogenized by douncing with an "A" pestle under conditions described above for floor plate homogenizations. Twenty-five percent homogenates were prepared and centrifuged at 2700 rpm (1000 X g) in an SA-600 rotor; the pellets were rehomogenized in one-half the original volume of homogenization buffer and recentrifuged. Supematants were pooled and volumes adjusted to a minimum of 30 ml; 26.3 ml of each was centrifuged at 50,000 rpm (230,000 X g, v ) in a 50.2Ti rotor (Beckman) for 30 min at 4 * C. Pellets were resuspended in less than 5 ml 50 mM Tris-HCl pH 7.5 using a dounce, and a one-half volume of 2 M NaCl, 50 mM Tris-HCl pH 7.5 solution was added. After mixing end-over-end at 4 "C overnight, the membranes were centrifuged at 70,000 rpm (200,000 X g av ) in an RP100-AT4 rotor (Dupont/Sorvall) for 23 min at 4 * C. Supematants were assayed after microdialysis against F12 medium (see below). E10 brains were found easier to dissect and yielded nearly as much activity. Biochemical purification Buffers: HBl: 320 mM sucrose, 10 mM HEPES-NaOH pH 7.5, 1 mM EDTA pH 8.0, 2 μg/ml leupeptin, 2 μg/ml aprotinin, 1 μg/ml pepstatin A. HB2: HBl + 1 mM PMSF; RB: 10 mM HEPES-NaOH pH 7.5, *2 mM EDTA pH 8.0, *4 μg/ml leupeptin, *4 μg/ml aprotinin, *2 μg/ml pepstatin A; SB1: 1.5 M NaCl, 10 mM HEPES-NaOH pH 7.5; SB2: 1.1 M NaCl, 10 mM HEPES-NaOH pH 7.5, *1 mM EDTA pH 8.0, *2 μg/ml leupeptin, *2 μg/ml aprotinin, *1 μg/ml pepstatin A; Al: 900 mM NaCl, 10 mM HEPES-NaOH pH 7.5; Bl: 2 M NaCl, 10 mM HEPES-NaOH pH 7.5; A2: 500 mM NaCl, 10 mM HEPES-NaOH pH 7.5, 100 μM CaCl 2 , 10 μM MnCl 2 ; B2: A2 + 700 mM N-acetylglucosamine; DB: 500 mM N-acetylglucosamine, 20 mM Tris-HCl pH 8.0; A3: 20 mM Tris-HCl pH 8.0; B3: A3 + 2 M NaCl; A4: 20 mM NaP ; pH 7.5 (dilute Na 2 HPO 4 , adjust pH with o-phosphoric acid), 1.5 M NaCl; B4: 20 mM NaPj pH 3.0 (dilute NaH 2 PO 4 , adjust pH with o-phosphoric acid), 1.5 M NaCl. Buffer pH was adjusted at ambient temperature; components indicated with an asterisk were added directly before use. All buffers were used ice cold except for Al, Bl, A3, B3, A4, and B4, which were used at 4 °C. Chromatography columns: Heparin-Sepharose CL-6B (HS CL-6B), column: Bio-Rad Econo-Column with flow adapter, 2.5 cm X 20 cm; resin: Heparin Sepharose CL-6B, Pharmacia. Wheat Germ Agglutinin Agarose (WGA Agarose), column: Bio-Rad Poly-Prep Column, 1 ml bed volume; resin: Wheat Germ Agglutinin Agarose, Vector Laboratories. Heparin-Sepharose High Performance (HSHP), column: Pharmacia HR 5 / 10 Column, 5 mm X 10 cm; resin: Heparin Sepharose High Performance, Pharmacia. Immobilized Metal Adsorption Chromatography (IMAC), column: Pharmacia HR 5 / 2 Column, 5 mm X 2.5 cm; resin: Chelating Sepharose High Performance, Pharmacia. Columns (except the WGA Agarose column, which was freshly poured with new resin for each purification run) were cleaned between runs with 6M guanidinium HC1 / 20 mM Tris-HCl pH 8.0 (except for the IMAC column, which in addition was then stripped with 0.5 M EDTA), and were stored in 0.1 % NaN 3 . All chromatography was performed at 4 "C. Purification procedure Day one (1) For a single purification run, on a single day approximately 1000 E 10 chick brains were dissected out into 1 liter L15 medium on ice over a period of approximately 2.5 hours. These dissected brains usually included a small portion of cervical spinal cord. (2) The brains were kept on ice prior to homogenization. After pouring off as much L15 as possible, approximately 25 ml brains were measured into a 50- ml polypropylene conical tube, and 25 ml Buffer HBl were added. The tube was capped and inverted several times to wash the brains. The brains were poured into a small kitchen strainer to drain off excess buffer, and then transferred into a 55- ml Potter-Ehrehjem homogenizer on ice. Twenty-five ml Buffer HBl and 0.5 ml 100 mM PMSF (in 2-propanol at ambient temperature) were added, and the brains were homogenized immediately at top speed: five up-and-down strokes followed by a pause on ice for 1 minute, followed by five additional up-and-down strokes. Usually, 1000 brains were homogenized in a total of eight batches, which were then pooled on ice, yielding approximately 360 ml of crude homogenate. (3) The crude homogenate was aliquoted into 50-ml Oak Ridge tubes and centrifuged at 2700 rpm (1000 X g) in an SA-600 rotor (Dupont/Sorvall) for 10 minutes at 4 "C. The supematants were pooled on ice (for a total of approximately 200 ml), and the pellets were vortexed to resuspend them. Fifteen ml Buffer HB2 was added to each tube per 40 ml crude homogenate originally present, and after mixing, the resuspended pellets were transferred sequentially to the homogenizer on ice and homogenized as before using one up-and-down stroke. Each was returned to its Oak Ridge tube and centrifuged at 2700 rpm in an SA-600 rotor for 10 minutes at 4 * C. The supematants were pooled with those obtained previously at this stage for a total of approximately 320 ml low speed supernatant (LSS). (4) The LSS was aliquoted into 40-ml Oak Ridge tubes and centrifuged at 8300 rpm (10,000 X g) in an SA-600 rotor for 10 minutes at 4 * C. The supematants were pooled on ice (a total of approximately 240 ml), and 25 ml Buffer HB2 was added to each tube per 40 ml LSS originally present. The pellets were resuspended by vortexing, and then sequentially transferred to the homogenizer on ice and homogenized as before using one up-and-down stroke. Each was returned to its Oak Ridge tube and centrifuged at 8300 rpm in an SA-600 rotor for 10 minutes at 4 * C. The supematants were pooled with those obtained previously at this stage for a total of approximately 450 ml medium speed supernatant (MSS). (5) The MSS was aliquoted into 26.3 ml capacity polycarbonate bottles and centrifuged at 50,000 rpm (230,000 X g, v ) in a 50.2 Ti rotor (Beckman) for 35 minutes at 4 β C. After discarding the supematants, 4 ml Buffer RB was added to each tube per 26 ml MSS originally present and the pellet was separated from the tube with repeated squirts of the added buffer by using a Pipetman P-1000. The buffer and pellet were transferred to a 50-ml conical tube on ice using a 10-ml pipette; the centrifuge tube was rinsed with 1 ml Buffer RB and this rinse pooled with the previously transferred material. The contents and rinses of every six centrifuge tubes were pooled into one conical tube. Sequentially, the contents of each conical tube were transferred into a 40-ml dounce and homogenized with 10 up-and-down strokes of an "A" pestle. This homogenate was transferred back into its 50-ml conical tube, frozen in liquid nitrogen, and stored at -80 °C. A total of approximately 120 ml high speed pellet (HSP) homogenate was obtained. Day two (6) The above steps were repeated on another day with another 1000 embryonic chick brains to yield HSP homogenate. Day three (7) The HSP homogenate derived from 2000 embryonic chick brains (in 50-ml conical tubes) was thawed quickly in a 37 * C circulating water bath and pooled in a 2 liter beaker on ice. Using a 3.5 X 0.5 inch magnetic stir bar, the homogenate was stirred in this beaker at medium speed (Thermolyne Nuova II, setting #6), and Buffer SBl was added at the rate of approximately 1.5 ml / min using a peristaltic pump until the conductance of 10 μl homogenate added to 1 ml of H 2 O was approximately 520 μS / cm. (Conductances were measured using a Radiometer CDM80 meter possessing a CDC 114 cell having a cell constant of 1 cm "1 .) At this point, the homogenate was stirred for 1 hour of additional time at a low setting (#3). The homogenate was aliquoted into five 75-ml capacity polycarbonate bottles and centrifuged at 35,000 rpm (100,000 X g ΪV ) in a 45Ti rotor (Beckman) for 2 hours at 4 * C. After discarding the supematants, 25 ml of Buffer SB2 was added to each tube, and the pellets were separated from the walls of the tube with repeated squirts of the added buffer by using a Pipetman P-1000. For each tube, the buffer and pellet were transferred into a 40-ml dounce; the centrifuge tube was rinsed with 15 ml Buffer SB2 and this rinse was then pooled with the buffer and pellet in the dounce. After homogenizing with 10 up-and-down strokes of an "A" pestle, the homogenates of the pellets were pooled in a 600-ml beaker on ice. Using a 2.5 X (5/16)-inch stir bar, this homogenate was then stirred on ice for 1 hour at a low setting (#4). A total of approximately 240 ml of low salt wash pellet (LSWP) homogenate was obtained. (8) The LSWP homogenate was aliquoted into four 45 Ti bottles and centrifuged at 35,000 rpm in a 45Ti for 2 hours at 4 'C. The supematants were recovered and stored at 4 °C overnight. Day four This supernatant was aliquoted into four bottles and centrifuged again at 35,000 rpm in a 45Ti rotor for 2 hours at 4 °C. All but approximately the last milliliter of supematant from each bottle was recovered and pooled on ice. A total of approximately 200 ml high salt extract (HSE) was obtained. (9) While stirring the HSE on ice (using a 2.5 X (5/16)-inch stir bar and a medium setting (#5)), ice cold 10 mM HEPES-NaOH pH 7.5 was added dropwise until the conductivity of 10 μl of this HSE added to 1 ml H 2 O was approximately 1000 μS / cm. (10) While diluting the HSE, the HS CL-6B column was equilibrated with 375 ml Buffer Al at a flow rate of 2.5 ml / min (column mn on a Bio-Rad Econo System). The diluted HSE was loaded onto the column at a flow rate of 1.5 ml / min. The flow-through was collected beginning 80 min after the start of loading and ending approximately 40 min after the last diluted HSE had been loaded onto the column. This flow-through fraction was the β Fraction. The β Fraction was frozen in 40-ml aliquots in liquid nitrogen and stored at -80 °C. The column was washed with a total of 300 ml Buffer Al at a flow rate of 1.5 ml /min. The bound protein was eluted with Buffer Bl at a rate of 1.5 ml /min. The peak of eluted protein was collected manually in a volume of approximately 30 ml using absorbance at 280 nm to monitor the column efflux for the beginning of the eluate peak. To the eluate fraction was added 30 μl of 1 mg / ml pepstatin A (in DMSO) and 60 μl of a solution of 1 mg / ml aprotinin and 1 mg / ml leupeptin. This eluate fraction was the Fraction, which was stored at 4 β C overnight. Day five (11) The Fraction was concentrated to a final volume of less than 1.5 ml in a 50-ml Amicon ultrafiltration cell at 55 psi nitrogen employing a YM30 membrane. The cell and membrane were washed with 0.5 ml Buffer A2 and pooled with the concentrate. The WGA Agarose column was washed with 50 ml of Buffer A2 under gravity flow. This column was loaded with the concentrate in 0.7 ml (maximum volume) batches, waiting 30 minutes between additional loadings. The column was then washed with two 1-ml volumes of Buffer A2, followed by 20 ml of Buffer A2. The column elution was begun with 0.7 ml Buffer B2, and the eluate was discarded. Elution was continued with an additional 0.3 ml Buffer B2, and the eluate was saved. After 1 hour, the elution was continued with 1 ml and then 0.7 ml Buffer B2, pooling with the previous eluate for a total WGA Agarose eluate of 2 ml. (12) The WGA Agarose eluate was diluted with 1.3 ml Buffer DB while undergoing gentle vortexing. The HSHP column was equilibrated with 20 ml 85% Buffer A3 / 15% Buffer B3 at 0.5 ml / min. (This column and IMAC column were n on a Waters 650E system having a model 441 Detector.) The diluted WGA Agarose eluate was loaded into the sample loop using a silanized syringe and injected onto the column at a flow rate of 0.1 ml / min. The column was then washed with 85% Buffer A3 / 15% Buffer B3 at this flow rate for a total of 90 minutes for the load and the wash combined. The valve was returned to "load" position, and the column was eluted with a linear gradient from 50% Buffer A3 / 50% Buffer B3 to 25% Buffer A3 / 75% Buffer B3 over a period of 200 minutes at 0.1 ml / min, collecting 0.5 ml fractions into 1.5 ml silanized polypropylene tubes. (13) To each of the six or seven fractions containing most of the protein eluting in the peak centered at approximately 1.5 mS / cm (10 μl fraction added to 1 ml H 2 O, corresponding to approximately 1.35 M NaCl), 22.6 μl 0.2 M NaH 2 PO 4 was added by layering the solution on the denser solution of the eluate, and then vortexing quickly. The fractions used were determined by counting from the end of the peak back to just at or over the half-height point on the leading side of the peak. The IMAC column was equilibrated at 0.5 ml / min with 75% Buffer A4 / 25% Buffer B4 for at least 10 minutes, and then the column was charged with 0.5 ml 0.1 M ZnSQ, at the same flow rate. The column was washed sequentially at 0.5 ml / min with 75% Buffer A4 / 25% Buffer B4 for 10 minutes, (then with the valve back at "load" position) 25% Buffer A4 / 75% Buffer B4 for 10 minutes, and finally with 75% Buffer A4 / 25% Buffer B4 for 20 minutes. The sample loop was loaded with the pooled, adjusted HSHP column fractions using a silanized syringe, and the contents of the loop were injected onto the column at 0.5 ml /min. After washing for an additional 1 minute before returning the valve to "load" position, the column was eluted with a linear gradient from 75% Buffer A4 / 25% Buffer B4 to 25% Buffer A4 / 75% Buffer B4 over a period of 20 min at 0.5 ml / min, with a 20 min wash at the end conditions thereafter. One ml fractions were collected into 1.5 ml silanized polypropylene tubes; ρ75 eluted isocratically (at a pH of approximately 6.5) after the flow-through, and p78 eluted in a peak centered on approximately pH 6.1. Preparation of fractions for assay In order to assay fractions from beyond the crude homogenate (which itself was not assayed) through the HSE fractions, 1 ml volumes were adjusted with 4M NaCl to 1M NaCl (if not already in high salt) and were mixed end-over-end at 4 * C for 1 hr. Salt-stripped membranes were removed by centrifugation for 100 min at 40,000 rpm (70,000 X g ΪV ) in a RP100-AT4 rotor (Dupont Sorvall) with microfuge tube adapters. Aliquots of these fractions and those from the HSE step through the end of the purification were adjusted to at least 1 M NaCl (if nescessary) and 1 mg / ml ovomucoid in order to stabilize the activity against freeze/thaw and dilution, and to prevent wheat germ agglutinin that had leached off the WGA Agarose column from (1) rebinding to the active protein during dialysis and (2) inhibiting outgrowth from the explants by itself. Ovomucoid alone has no effect in the El 1 or E13 assays. Volumes (between 0.1 - 0.2 ml) of fractions or dilutions of fractions to be assayed for activity were prepared by dialysis against F12 medium at a flow rate of 1 ml / min for at least three hours in a Gibco/BRL microdialyzer using Spectrapor 2 (Spectmm) dialysis membrane. Routinely, samples were brought up to a final volume of 0.4 ml with F12 medium (and 0.2 ml β Fraction dialyzed against F12, if the fractions were from a stage in the purification beyond the HS CL-6B column), and other components required to complete the medium (Tessier-Lavigne et al, 1988). Samples were warmed to 37 * C before addition to the explant cultures. Ell and El 3 assays were prepared as described above, except that the cultures were incubated in complete medium for up to 8 hr before the addition of the warmed samples. SDS-PAGE Trichloroacetic acid (TCA) precipitation of proteins and SDS-PAGE were performed as described previously (Serafini et al, 1991). Protein microsequencing TCA precipitation: p78 A total of 11.75 ml from IMAC fractions (from three separate purification runs) containing p78 were made 0.015% in deoxycholate by the addition of 2% deoxycholate, and were precipitated in ten batches of no more than 1.25 ml in two 12 X 75 mm borosilicate glass tubes. To each 1.25 ml (or lower) volume was added an equal volume of 0.015% deoxycholate (to dilute the NaCl present in the fractions) and a two-thirds volume of 24% TCA. After incubation for 1 hr on ice, the precipitate was collected by centrifugation for 30 min at 3000 rpm (2060 X g) in a GH-3.7 rotor (Beckman). The remaining batches were precipitated sequentially in the two tubes after removal of the supematants. After the final precipitation, the pellets were resuspended by vigorous vortexing in 1 ml ice cold 6% TCA (to remove NaCl), and an additional 1 ml 6% TCA was used to wash pellet fragments down from the sides of the tube. The rinsed precipitate was collected by centrifugation as before, and the supematants were aspirated. Deoxycholate and TCA were then removed by addition of 1 ml acetone (at -20 * C) and vortexing until the white precipitate was no longer apparent. The precipitated p78 was collected by centrifugation as before, the supematants were aspirated, and the pellets were dried for 15 min at 37 • c. TCA precipitation: p75 To increase the amount of p75 available for microsequencing, fractions from two HSHP chromatography runs containing predominantly p75 (i.e., those three fractions in each HSHP n collected just before those pooled for the last purification step) were pooled, adjusted with 0.2 M NaH 2 PO 4 , and chromatographed on the IMAC column as previously described. The p75 present in a total of 14.9 ml from IMAC fractions from four purification mns was TCA precipitated as described above for p78. CNBr proteolysis In order to obtain internal amino acid sequence from p78 and p75, peptides were generated by cyanogen bromide (CNBr) cleavage. The pellets of TCA precipitated protein were resuspended in 50 μl of a solution of 50 mg / ml CNBr in 70% formic acid, and were pooled and incubated overnight in the dark at ambient temperature. The formic acid was removed by evaporation in a SpeedVac (Savant). The residue was resolubilized in 50 μl deionized H 2 O and evaporated again to dryness in order to remove the remaining formic acid. Gel electrophoresis and electroblotting The CNBr-generated peptides were isolated essentially as described previously (Kennedy et al, 1988). The residue remaining after the final evaporation was solubilized in SDS-PAGE sample buffer containing 25 mM Tris base, loaded into a 1.5 cm well on a 1.5mm thick, 20 cm long 15 % polyacrylamide gel, and electrophoresed until the dye front just reached the bottom of the gel. Sodium thioglycolate (0.2 mM) was added to the electrophoresis buffer in the cathode chamber in order to scavenge free radicals remaining in the gel. Peptides were blotted onto a ProBlott membrane (Applied Biosystems) and visualized essentially as described (Matsudaira et al, 1987). Briefly, the gels were soaked for ten minutes in Transfer Buffer (10 mM 3- (cyclohexylamino)-l-propanesulfonic acid (CAPS) pH 11.0 / 10% methanol). ProBlott membranes were cut to size, wetted with 100% methanol, and equilibrated with Transfer Buffer. After assembly of the blotting sandwich, electroblotting was performed in a Bio-Rad Trans-Blot Cell at 1.0 A for 30 min at 4 β C. Following transfer the blots were washed with deionized H 2 O for 5 min, stained for 5 min in 0.1 % Coomassie Brilliant Blue R-250 in 50% methanol, and then destained with 50% methanol / 10% acetic acid. After washing with water, the blots were air dried, and the peptide bands were excised and stored in 0.1 % trifluoroacetic acid at -20 'C. Prior to sequencing, the excised bands were feathered with a scalpel. Protein sequencing Peptide sequencing was performed on a Porton Instruments automated gas phase sequencer (Model PI 2020G) equipped with an on line analyzer for phenylthiohydantoin (PTH)-derivatized amino acids. N-terminal protein sequencing A volume of 0.6 ml (plus 0.4 ml water) p75-containing pooled IMAC fractions and 1 ml p78-containing IMAC fractions were separately TCA precipitated as described previously. After aspirating the acetone wash (and without any drying), the precipitated protein in each case was dissolved in 15 μl 70% formic acid and applied 3 μl at a time to a 2 X 5 mm piece of ProBlott membrane, allowing the membrane to dry between additions. The tubes were washed with an additional 15 μl 70% formic acid, which was then applied to the membranes. Sequencing was performed directly on these membrane pieces after feathering them. N-terminal sequencing was also performed on impure p75 / p78 subjected to SDS-PAGE and electroblotting as outlined above, with the p75 and p78 bands excised separately. RNA isolation Sixty-two E10 chick brains were dissected as described above and snap frozen in liquid nitrogen. Tissue was homogenized using a Polytron (Brinkmann) and total cellular RNA was isolated as described (Auffray and Rougeon, 1980). A total of 15.9 mg of total cellular RNA was obtained, a yield of 256 μg of total RNA per 0.22 g brain. RNA was isolated from total cellular RNA using oligo dT cellulose (Collaborative Research) as described (Ausubel et al., 1990). Seven and one-half mg of E10 chick brain RNA provided 353 μg poly(A)+ RNA, a yield of approximately 5%. PCR generation of a fragment of the gene encoding p78 Twenty-five μg E10 chick brain poly(A) + RNA was reverse transcribed in a 100 μl reaction using 1000 U M-MLV (Gibco/BRL) under standard conditions (Ausubel et al, 1990). The RNA was heated to 95 β C for 5 min prior to its addition to a reaction mix lacking enzyme. Enzyme was added, and after 10 min at ambient temperature the reaction was incubated for 1 hr at 37 * C. The reaction was then heated to 95 * C for 5 min and was quenched on ice and stored at -20 'C. Gel-purified, degenerate oligonucleotides designed from what were considered unambiguous stretches of amino acid sequence were used in two-stage nested PCR to obtain a fragment of the gene encoding p78. PCR was performed in a 50 μl reaction containing IX PCR buffer (per Perkin Elmer Cetus), 0.1 mM dNTPs, 1 μM sense primer, 1 μM antisense primer, 2 μl cDNA synthesis reaction, and 0.5 μl (2.5 U) Taq DNA polymerase (Perkin Elmer Cetus). The second stage reaction was identical in composition except that the cDNA synthesis reaction was replaced by 1 μl of a 1: 10 dilution of the first reaction. An MJ Research MiniCycler with temperature probe control was used for PCR. Taq polymerase was added after the samples had been brought to 92 °C; the cycling program for both reactions was 95 °C for 30 s, 37 'C for 30 s, increase by 1 β C every 5 s to 72 °C, 72 "C for 1 min, and twenty-nine iterations of the cycle followed by 15 min at 72 * C. One half of the second PCR reaction was electrophoresed in a 1.5 mm thick 15% polyacrylamide minigel, and the single observed band of approximately 100 bp was excised and eluted in 100 μl H 2 O over 7.5 hr in a 37 "C shaking incubator. The fragment was cloned into the pCRII vector using a TA-cloning kit (Invitrogen). Transformants were screened with PCR amplification across the cloning site, and four positive clones with 92 bp inserts were sequenced to yield 62 bp of unambiguous sequence of the gene encoding p78. PCR generation of a fragment of the gene encoding p75 Two-stage nested PCR was also used to obtain a fragment of the gene encoding p75. The first stage consisted of four reactions, each having as sense primer the same degenerate oligonucleotide pool that was used in the first stage of cloning the p78 gene fragment, and having four different pools of degenerate oligonucleotides based on a single amino acid sequence as the antisense primer. PCR was performed as described above except that 1 μl of a cDNA synthesis reaction was used, and the Taq polymerase was added after the reaction had been heated to 94 °C. The temperature probe was not used to control the cycling program, which consisted of 97 * C for 1 min, X 'C for 1 min, 74 β C for 1 min, thirty-four more iterations of the cycle, followed by 74 'C for 20 min; "X" equalled 35, 40, 45, 50, 55, or 60. Twenty μl of each reaction was analyzed on a 2% agarose gel, and predominating in reactions using two of the four antisense pools (but present in all) was a product of approximately 630 bp that only appeared at the higher (more stringent) annealing temperatures, all of which would be expected for a bona fide p75 gene fragment. For each of the four reactions carried out with 55 * C annealing, this 630 bp product was electrophoresed into 0.8% low melting point agarose. The four second stage reactions were performed as were the first stage reactions, except that the input DNA consisted of 0.5 μl of melted low melting point agarose containing the 630 bp products. In each case, a single band of approximately 380 bp was amplified. Fifteen μl from each of the reactions was combined, phenol/chloroform/isoamyl extracted, and the DNA precipitated. The isolated 380 bp product was digested with Sac I (which recognizes a site at this point in the gene for p78), and that small portion which remained uncut was isolated using Geneclean (BiolOl), reamplified, redigested with Sac I, and cloned into the pCRII vector as described above. Transformants were screened with PCR across the cloning site, and two positives contained 377 bp inserts yielding 341 bp of unambiguous sequence of the gene encoding p75. cDNA cloning Library construction cDNA libraries, both oligo dT primed and specifically primed, were constmcted using the ZAP cDNA Gigapack II Gold Cloning Kit (Stratagene) according to the manufacturer's instructions. cDNAs were size selected using a BRL cDNA size selection column in order to insure an insert size greater than 500 bp. In this way, an E10 chick brain cDNA library was constmcted in the lambda ZAP vector using as starting material 5 μg of E10 chick brain poly(A) + RNA. For the isolation of 5' and 3' sequences, additional libraries were constructed using sequence specific first strand synthesis primers. Sequence obtained using 3' RACE (see below) was used to design a p78 oligonucleotide complimentary to sequence 3' of the translational stop codon with an attached 5' Xho I site, primer WI. Primer WI was then used to prime the synthesis of first strand cDNA for a specific p78 library. Similarly, sequence 3' to the translational stop site in the p75 cDNA and sequence in the 5' end of the Clone 25 p75 cDNA were used to construct two primers, p75Xl and p75X2, to prime the first strand synthesis of cDNA libraries designed to obtain the missing 5' sequence of p75. cDNAs generated using sequence specific primers were cloned directly into Eco RI / Xho I digested pBluescript SK(+) vector (Stratagene). 3' RACE Sequence corresponding to the 3' end of the p78 cDNA was amplified and cloned using the RACE protocol as described by Frohman and Martin (1989). The 3' poly(T) primer and primers R; and R„ were used exactly as described, and the p78 specific 5' primers R5, R6, and R7 were used for nested PCR reactions. Vent DNA polymerase (New England Biolabs) was used for RACE reactions using the buffer provided by NEB and a final MgSO 4 concentration of 4 mM. Probe design and synthesis Probes used to screen the libraries were of two types: (1) random primed probes generated from gel-purified templates using a kit (Boehringer Mannheim) and (2) probes isotopically labelled by the incorporation of a 32 P-dCTP during PCR. The reaction conditions for the amplification of a p78 61 bp probe (probe Zl) were as follows: Two μM each of primers p78ol00 and p78ol01; 50μM dTTP, dATP, dGTP; lOOμCi a 32 P-dCTP (17 pmoles at 6000 Ci / mM); IX PCR buffer; and 2.5 U Taq DNA polymerase. For all PCR probe generation, the Taq polymerase was added after the reactions had been brought to the denaturation temperature. The amplification conditions were: (1) 95 * C for 30 s, (2) 60 * C for 30 s, (3) 72 * C for 30 s, with nine iterations of the program. The reaction conditions used to generate a p78 584 bp probe (probe Z2) were as follows: primers Pl and P2 each at 0.1 μM; 0.1 mM dATP, dTTP and dGTP; 3.4 μM dCTP; 200 μCi a 32 P-dCTP (33 pmoles at 6000 Ci / mM); IX PCR buffer; and 2.5 U Taq polymerase. The amplification conditions were: (1) 94 * C for 30 s, (2) 64 * C for 45 s, (3) 72 °C for 1 min, with 24 iterations of the program. The reaction conditions used to generate a p75 258 bp probe (probe Z3) using primers Q3 and Q4 were the same as those for probe Z2 with the exception of using dCTP at 1.25 μM. Reaction conditions for probe Z4 synthesis were essentially as described above for probe Z2, but used the primers Ql and Q2 to generate a 243 bp probe specific for p78. For a 5' p75 probe (probe Z5) synthesis, the reaction conditions were the following: primers OCM1 and OCM2 at 0.1 mM; 25 μM dATP, dGTP, dTTP; 2.5 μM dCTP; 100 μCi a 32 P-dCTP (17 pmoles at 6000 Ci / mM); IX Taq buffer; and 5 U Taq. The amplification conditions were as follows: (1) 94 °C for 30 s, (2) 48 °C for 40 s, (3) 72 °C for 40 s, with 24 iterations of the program. Library screening For screening, phage plaques or bacterial colonies were lifted onto duplicate filters (Hybond-N, Amersham), denatured and lyzed by autoclaving at 100 * C for 1 min, and the DNA UV crosslinked to the membrane. Before prehybridization the filters were washed in IX SSC, 0.5% SDS to remove any residual protein. Probe was denatured before use at 95 °C for 5 minutes, and then chilled on ice or directly added hot to hybridization mixes. Using probe Zl at 1 X IO 6 cpm / ml, 1 X IO 6 clones of the E10 chick brain cDNA library were screened at high stringency (hybridization conditions: 6X SSC, 0.5% SDS, 2X Denhardt's, 100 μg / ml salmon sperm DNA at 55 "C; wash conditions: IX SSC, 0.5% SDS at 55 °C). This initial screen identified a single internally primed 1 kb clone corresponding to p78, Clone 20. A second 1 X 10 6 clones were screened with probes Z2 and Z3. In this screen, the filters were again screened at high stringency (hybridization conditions: 6X SSC, 5X Denhardt's, 0.5% SDS, 100 μg / ml salmon sperm DNA at 65 °C, wash conditions: 0.1X SSC, 0.1 % SDS, 65 * C) with 1 X IO 6 cpm / ml of each probe. This second screen identified one cDNA corresponding to p78, Clone 29, and four cDNAs corresponding to p75: Clones 22, 25, 28, 34. The filters representing the 2 X IO 6 ElO chick brain clones were stripped and rescreened using probes (at 1 X 10 6 cpm / ml) randomly primed on gel isolated cDNAs of Clones 13, 25, and 29 using essentially the hybridization conditions described by Church and Gilbert (1980): prehybridization and hybridization in 500 mM NaP ; pH 7.2, 1 % SDS, 1 mM EDTA at 65 * C, with washing in 40 mM NaP; pH 7.2, 1 % SDS at 65 °C. This screen identified an additional four partial p75 cDNAs. Three further cDNAs corresponding to p75, Clones 6, 7, and 9, were identified in a screen of an additional 1 X IO 6 clones of the ElO chick brain cDNA library using probe Z3 (at 1 X IO 6 cpm / ml) and Church hybridization conditions. An additional 1.7 kb p78 clone, Clone 13, was isolated by screening 2 X IO 6 lambda ZAP clones of an amplified E2.5 spinal cord cDNA library with probe Z4 using the above conditions. Phage were isolated and inserts excised in vivo and recircularized into pBluescript II SK(-) as recommended by Stratagene. Specifically primed cDNA libraries constmcted in pBluescript were screened using Church conditons with probe Z4 or probe Z5, as appropriate, to identify clones containing cDNAs encoding the full coding sequences of p78 and p75. DNA sequencing Nested deletions for sequencing were generated using exo III digestion as described (Ausubel et al., 1990). Sequence was also obtained in some instances by subcloning small fragments or by using specific internal oligonucleotide primers. Dideoxysequencing was performed using the Sequenase kit (USB). In addition, sequence compressions were resolved by a combination of dlTP sequencing (Sequenase USB) and Exo(-)PFU Cyclist DNA sequencing (Stratagene). Oligonucleotide synthesis and purification Oligonucleotides were synthesized using a Cyclone Plus DNA Synthesizer (Millipore). Oligonucleotides were polyacrylamide gel purified using standard methods (Sambrook at al., 1989). Northern analysis For Northern blot analysis, 1-5 μg of poly(A) + RNA from various chick tissues was denatured with formaldehyde, separated on a 1 % agarose gel containing formaldehyde, and blotted to Hybond N (Amersham) as described (Sambrook et al., 1989). Probes were randomly primed from gel isolated p78 and p75 cDNA templates. Southern analysis of genomic DNA Chicken genomic DNA was isolated as follows (see Laird, et al, 1991): Seven Ell chick brains were dissected out and placed into 25 ml of 100 mM Tris- HCl pH 8.3, 5 mM EDTA, 0.2% SDS, 200 mM NaCl, 100 μg / ml proteinase K in a 50-ml conical tube; after 14.5 hr incubation at 55 °C with agitation, 25 μg DNase-free RNase A was added and the incubation continued for another 3 hr. The solution was centrifuged at 8310 rpm (10,000 X g) in an SA-600 rotor at 4 β C for 15 min; supematant was poured into an equal volume of 2-propanol and the tubes were mixed gently end-over-end. Genomic DNA was removed from the tube using a plastic pipette tip, and was dissolved in 2 ml TE overnight at 55 °C, yielding 1.25 mg / ml DNA. Ten μg genomic DNA was digested with 30 U Eco RI in 20 μl over a 5 hr period, electrophoresed in a 0.8% agarose gel, and then transferred to Hybond-N (Amersham) using standard conditions. The blot was probed sequentially with random-primed radiolabelled probes made with Clone 13 (for p78) and Clone 25 (for p75) as templates using hybridization conditions described by Church and Gilbert (1980). In situ hybridization In situ hybridization was performed essentially as described in Ausubel et al., eds. (1990). Expression of recombinant p78 and p75 Sequences encoding the entire coding region of either p78 or p75 in an Eco RI / Xho I fragment are subcloned into the COS cell expression vector pcDNAl (Invitrogen) yielding the plasmids p78EXCl (for p78) and ρ75EXC2 (for ρ75). Early passage COS cells are seeded at 2.5 X IO 5 cells per 35 mm well in six-well plates, and are transfected approximately 18-20 hr later with 1 μg p78EXCl or p75EXC2 DNA (prepared by PEG precipitation) using 6 μl Lipofectamine (Gibco/BRL) according to the manufacturer's instructions. Complete medium (DME-H21) is conditioned for at least 24 h in order to accumulate expressed protein. At the end of the conditioning period, medium and cells are harvested, and the cells are extracted with 1 M NaCl to extract adsorbed recombinant protein. Recombinant protein is purified through methods based on the established purification of the proteins from embryonic chick brain. Aggregated COS cells secreting netrins are conveniently used to screet netrins, netrin mutants and netrin derived peptides for the ability to elicit axon outgrowth; see e.g. Kennedy et al. (1994) Cell 78:425, Figure 4. Recombinant protein is also obtained using a baculovirus expression system (Ausubel, 1990), and is purified as described above. REFERENCES CITED IN EXAMPLES Auffray et al. (1980) Eur. J. Biochem. 107:303-314; Ausubel et al. eds. (1990) Current Protocols in Molecular Biology. Greene Publishing Associates and Wiley- Interscience; Calof et al. (1991) J. Cell Biol. 115:779-794; Church et al. (1984) Proc. Natl. Acad. Sci. USA 81: 1991-1995; Cooke et al. (1987) Nature 327:339- 341; Engel (1989) FEBS Letters 251: 1-7; Frohman et al. (1989) Technique 1:165- 170; Kennedy et al. (1988a) Proc. Natl. Acad. Sci. USA 85:7008-7012; Kleinman et al. (1993) Vitamins and Hormones 47: 161-187; Laird et al. (1991). Nucl. Acids Res. 19:4293; Massague (1991) Curr. Biol. 1:117-119; Matsudaira (1987) J. Biol. Chem. 262: 10035-10038; Placzek et al. (1990a) Development 110:19-30; Placzek et al. (1990b) Cold Spring Harbor Svmposia on Quantitative Biology 55:279-302; Sambrook (1989) Molecular cloning: a laboratory manual. 2nd ed. Cold Spring Harbor Lab., NY; Serafini et al. (1991) Nature 349:215-220; Tessier-Lavigne et al. (1988) Nature 336:775-778; von Heijne (1986) Nucl. Acids Res. 14:4683-4690; Walter et al. (1987) Development 101:685-96; Yurchenco and Cheng (1993) Biol. Chem. 268: 17286-17299. All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: THE REGENTS OF THE UNIVERSITY OF CALIFORNIA COLUMBIA UNIVERSITY (ii) TITLE OF INVENTION: NEURAL AXON OUTGROWTH MODULATORS (iii) NUMBER OF SEQUENCES: 6 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: ROBBINS, BERLINER & CARSON (B) STREET: 201 North Figueroa Street, 5th Floor (C) CITY: Los Angeles (D) STATE: California (E) COUNTRY: USA (F) ZIP: 90012-2628 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentin Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: (C) CLASSIFICATION: (viii) ATTORNE /AGENT INFORMATION: (A) NAME: Berliner, Robert (B) REGISTRATION NUMBER: 20,121 (C) REFERENCE/DOCKET NUMBER: 5555-263 (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: (213) 977-1001 (B) TELEFAX: (213) 977-1003 (C) TELEX: (2) INFORMATION FOR SEQ ID Nθ:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1926 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (xi) SEQUENCE DESCRIPTION: SEQ ID Nθ:l: ATGCCGCGGA GGGGCGCGGA GGGGCCGCTC GCCCTGCTGC TGGCGGCCGC GTGGCTGGCA 60 CAGCCGCTGC GAGGCGGCTA CCCCNNNCTG AACATGTTCG CCGTGCAGAC GNCAGCCGAC 120 CCCTGCTACG ACGAGCACGG GCTGCCCCNC CGCTGCATCC CGGACTTCGT CAACTCGGCC 180 TTCGGCAAGG AGGTGAAGGT GTCGAGCACC TGCGGGAAGC CGCCGTCGAG GTACTGCGTG 240 GTGACGGAGA AGGGCGAGGA GCAGGTCCGC TCGTGCCACC TCTGCAACGC CTCCGACCCC 300 AAGCGCGCCC ACCCGCCCTC CTTCCTCACC GACCTCAACA ACCCGCACAA CCTGACGTGC 360 TGGCAGTCCG ACAGCTACGT GCAGTACCCG CACAACGTCA CCCTCACGCT GTCCCTCGGC 420 AAGAAGTTCG AGGTGACCTA CGTGAGCCTG CAGTTCTGCT CGCCGCGCCC CGAGTCCATG 480 GCCATCTACA AGTCCATGGA CTACGGCAAG ACGTGGGTGC CCTTCCAGTT CTACTCCACG 540 CAGTGCCGCA AGATGTACAA CAAGCCGAGC CGCGCCGCCA TCACCAAGCA GAACGAGCAG 600 GAGGCCATCT GCACCGACTC GCACACCGAC GTGCGGCCCC TCTCCGGCGG CCTCATCGCC 660 TTCAGCACCC TGGACGGCCG CCCCACCGCC CACGACTTCG ACAACTCGCC CGTGCTGCAG 720 GACTGGGTGA CGGCCACCGA CATCAAGGTG ACCTTCAGCC GCCTGCACAC CTTCGGCGAC 780 GAGAACGAGG ACGACTCCGA GCTCGCCCGC GACTCCTACT TCTACGCCGT GTCCGACCTG 840 CAGGTCGGCG GGCGCTGCAA GTGCAACGGG CACGCGTCCC GCTGCGTCCG CGACCGCGAC 900 GACAACCTGG TGTGCGACTG CAAGCACAAC ACGGCCGGGC CCGAGTGCGA CCGCTGCAAA 960 CCCTTCCACT ACGACCGGCC CTGGCAGAGG GCGACCGCCC GAGAGGCCAA CGAGTGCGTG 1020 GCCTGCAACT GCAACCTGCA TGCACGGCGC TGCCGCTTCA ACATGGAGCT GTACAAGCTG 1080 TCGGGCAGAA AGAGCGGCGG TGTCTGCCTC AACTGCCGGC ACAACACGGC CGGGCGGCAC 1140 TGCCACTACT GCAAGGAAGG CTTCTACCGC GACCTCAGCA AACCCATCTC CCACCGCAAG 1200 GCCTGCAAAG AGTGCGATTG CCATCCCGTG GGCGCCGCCG GCCAAACCTG CAACCAAACC 1260 ACGGGGCAGT GTCCATGCAA GGACGGCGTC ACCGGCATCA CCTGCAACCG CTGCGCCAAG 1320 GGCTACCAGC AGAGCCGCTC GCCCATTGCC CCCTGCATAA AGATCCCCGC CGCGCCGCCC 1380 CCCACAGCTG CCAGCAGCAC GGAGGAGCCT GCAGACTGTG ACTCGTACTG CAAAGCCTCC 1440 AAGGGGAAGC TGAAGATCAA CATGAAGAAG TACTGCAAGA AGGACTACGC TGTGCAGATC 1500 CACATCCTGA AAGCGGAAAA AAATGCCGAC TGGTGGAAGT TCACCGTCAA CATCATCTCT 1560 GTCTACAAAC AGGGCAGCAA CCGGCTGCGG CGCGGGGACC AGACCCTGTG GGTGCACGCC 1620 AAGGACATCG CCTGCAAGTG CCCCAAGGTG AAGCCCATGA AGAAGTACCT CCTGCTGGGC 1680 AGCACCGAGG ACTCTCCCGA CCAGAGCGGC ATCATCGCGG ACAAGAGCAG CCTGGTGATC 1740 CAATGGCGGG ACACGTGGGC ACGGCGGCTG CGGAAGTTCC AGCAGAGGGA GAAGAAGGGG 1800 AAGTGTAGGA AGGCGTAGGG AGGAGCGGTG ATGGACTGAG CGCTGCCGGG TGCGGGCGGG 1860 GGGTGGGCGC AGGGGGCTCA CGGCATCTCG TATTGAGGGA TGGAAGGGGA AAAAAAACAC 1920 GAAACC 1926 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 605 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID Nθ:2: Met Pro Arg Arg Gly Ala Glu Gly Pro Leu Ala Leu Leu Leu Ala Ala 1 5 10 15 Ala Trp Leu Ala Gin Pro Leu Arg Gly Gly Tyr Pro Xaa Leu Asn Met 20 25 30 Phe Ala Val Gin Thr Xaa Ala Asp Pro Cys Tyr Asp Glu His Gly Leu 35 40 45 Pro Xaa Arg Cys lie Pro Asp Phe Val Asn Ser Ala Phe Gly Lys Glu 50 55 60 Val Lys Val Ser Ser Thr Cys Gly Lys Pro Pro Ser Arg Tyr Cys Val 65 70 75 80 Val Thr Glu Lys Gly Glu Glu Gin Val Arg Ser Cys His Leu Cys Asn 85 90 95 Ala Ser Asp Pro Lys Arg Ala His Pro Pro Ser Phe Leu Thr Asp Leu 100 105 110 Asn Asn Pro His Asn Leu Thr Cys Trp Gin Ser Asp Ser Tyr Val Gin 115 120 125 Tyr Pro His Asn Val Thr Leu Thr Leu Ser Leu Gly Lys Lys Phe Glu 130 135 140 Val Thr Tyr Val Ser Leu Gin Phe Cys Ser Pro Arg Pro Glu Ser Met 145 150 155 160 Ala lie Tyr Lys Ser Met Asp Tyr Gly Lys Thr Trp Val Pro Phe Gin 165 170 175 Phe Tyr Ser Thr Gin Cys Arg Lys Met Tyr Asn Lys Pro Ser Arg Ala 180 185 190 Ala lie Thr Lys Gin Asn Glu Gin Glu Ala lie Cys Thr Asp Ser His 195 200 205 Thr Asp Val Arg Pro Leu Ser Gly Gly Leu lie Ala Phe Ser Thr Leu 210 215 220 Asp Gly Arg Pro Thr Ala His Asp Phe Asp Asn Ser Pro Val Leu Gin 225 230 235 240 Asp Trp Val Thr Ala Thr Asp lie Lys Val Thr Phe Ser Arg Leu His 245 250 255 Thr Phe Gly Asp Glu Asn Glu Asp Asp Ser Glu Leu Ala Arg Asp Ser 260 265 270 Tyr Phe Tyr Ala Val Ser Asp Leu Gin Val Gly Gly Arg Cys Lys Cys 275 280 285 Asn Gly His Ala Ser Arg Cys Val Arg Asp Arg Asp Asp Asn Leu Val 290 295 300 Cys Asp Cys Lys His Asn Thr Ala Gly Pro Glu Cys Asp Arg Cys Lys 305 310 315 320 Pro Phe His Tyr Asp Arg Pro Trp Gin Arg Ala Thr Ala Arg Glu Ala 325 330 335 Asn Glu Cys Val Ala Cys Asn Cys Asn Leu His Ala Arg Arg Cys Arg 340 345 350 Phe Asn Met Glu Leu Tyr Lys Leu Ser Gly Arg Lys Ser Gly Gly Val 355 360 365 Cys Leu Asn Cys Arg His Asn Thr Ala Gly Arg His Cys His Tyr Cys 370 375 380 Lys Glu Gly Phe Tyr Arg Asp Leu Ser Lys Pro lie Ser His Arg Lys 385 390 395 400 Ala Cys Lys Glu Cys Asp Cys His Pro Val Gly Ala Ala Gly Gin Thr 405 410 415 Cys Asn Gin Thr Thr Gly Gin Cys Pro Cys Lys Asp Gly Val Thr Gly 420 425 430 lie Thr Cys Asn Arg Cys Ala Lys Gly Tyr Gin Gin Ser Arg Ser Pro 435 440 445 He Ala Pro Cys He Lys He Pro Ala Ala Pro Pro Pro Thr Ala Ala 450 455 460 Ser Ser Thr Glu Glu Pro Ala Asp Cys Asp Ser Tyr Cys Lys Ala Ser 465 470 475 480 Lys Gly Lys Leu Lys He Asn Met Lys Lys Tyr Cys Lys Lys Asp Tyr 485 490 495 Ala Val Gin He His He Leu Lys Ala Glu Lys Asn Ala Asp Trp Trp 500 505 510 Lys Phe Thr Val Asn He He Ser Val Tyr Lys Gin Gly Ser Asn Arg 515 520 525 Leu Arg Arg Gly Asp Gin Thr Leu Trp Val His Ala Lys Asp He Ala 530 535 540 Cys Lys Cys Pro Lys Val Lys Pro Met Lys Lys Tyr Leu Leu Leu Gly 545 550 555 560 Ser Thr Glu Asp Ser Pro Asp Gin Ser Gly He He Ala Asp Lys Ser 565 570 575 Ser Leu Val He Gin Trp Arg Asp Thr Trp Ala Arg Arg Leu Arg Lys 580 585 590 Phe Gin Gin Arg Glu Lys Lys Gly Lys Cys Arg Lys Ala 595 600 605 (2) INFORMATION FOR SEQ ID NO:3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 2783 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: NTCCTGCGCC TGCTGCTCAC CACCAGCGTG CTCCGCCTGG CACGAGCTGC AAACCCCTTC 60 GTGGCTCAGC AGACTCCCCC AGACCCCTGC TACGATGAGA GCGGGGCTCC CCCGCGCTGC 120 ATCCCCGAGT TCGTCAACGC CGCCTTTGGG AAGGAGGTGC AGGCTTCCAG CACCTGTGGG 180 AAGCCCCCAA CACGGCACTG CGATGCCTCG GACCCCCGCC GAGCCCACCC ACCCGCCTAC 240 CTGACCGACC TCAACACCGC CGCCAACATG ACGTGCTGGC GCTCCGAGAC CCTGCACCAC 300 CTGCCCCACA ACGTCACCCT CACCCTTTCC CTCGGCAAGA AGTTTGAGGT GGTCTACGTC 360 AGCCTCCAGT TCTGCTCGCC CCGGCCGGAG TCCACCGCCA TCTTCAAGTC CATGGACTAC 420 GGCAAGACGT GGGTCCCCTA CCAGTACTAC TCCTCGCAGT GCCGCAAGAT CTACGGCAAG 480 CCCAGCAAGG CCACCGTCAC CAAGCAGAAC GAGCAGGAGG CGCTGTGCAC CGATGGCCTC 540 ACCGACCTCT ACCCGCTCAC TGGCGGCCTC ATCGCCTTCA GCACGCTCGA CGGGCGGCCC 600 TCGGCCCAGG ACTTCGACAG CAGCCCTGTG CTGCAGGACT GGGTGACGGC CACCGACATC 660 CGGGTGGTGT TCAGCCGTCC CCACCTCTTC CGCGAGCTGG GGGGCCGCGA GGCTGGCGAG 720 GAGGACGGGG GGGCCGGGGC CACCCCCTAC TACTACTCGG TGGGCGAGCT GCAGGTCGGC 780 GGGCGCTGCA AGTGCAACGG GCACGCCTCG CGCTGCGTCA AGGACAAGGA GCAGAAGCTG 840 GTGTGTGACT GCAAGCACAA CACCGAGGGG CCCGAGTGCG ACCGCTGCAA GCCCTTCCAC 900 TACGACCGGC CGTGGCAGCG GGCCAGCGCC CGCGAGGCCA ACGAGTGCCT GGCCTGCAAC 960 TGCAACCTGC ACGCTCGGCG CTGCCGCTTC AACATGGAGC TGTATAAGCT GTCCGGCAGG 1020 AAGAGCGGCG GCGTTTGCCT CAACTGCCGA CACAACACGG CTGGGAGGCA CTGCCACTAC 1080 TGCAAGGAGG GCTTCTACCG GGACCTCAGC AAGTCCATCA CGGACCGCAA GGCCTGCAAA 1140 GCCTGTGACT GCCACCCAGT TGGTGCTGCT GGCAAGACCT GCAACCAAAC AACAGGGCAG 1200 TGCCCGTGCA AGGACGGCGT GACCGGCCTC ACCTGCAACC GCTGCGCCAA GGGCTTCCAG 1260 CAGAGCCGCT CGCCTGTGGC CCCCTGCATC AAGATCCCTG CCATCAACCC GACCTCTCTT 1320 GTCACCAGCA CGGAGGCACC TGCAGACTGT GACTCCTACT GCAAGCCAGC CAAAGGCAAC 1380 TACAAGATTA ACATGAAGAA GTACTGCAAG AAGGATTACG TGGTCCAAGT GAACATTTTG 1440 GAAATGGAGA CGGTGGCCAA CTGGGCCAAG TTCACCATCA ACATCCTCTC TGTCTACAAG 1500 TGCCGCGACG AGCGGGTCAA GCGCGGAGAC AACTTCTTGT GGATCCACCT CAAGGACCTG 1560 TCCTGCAAGT GCCCCAAAAT CCAGATCAGC AAGAAGTACC TGGTGATGGG CATCAGCGAG 1620 AACTCCACCG ACCGGCCGGG ACTGATGGCC GACAAGAACA GCCTGGTCAT CCAGTGGAGG 1680 GACGCCTGGA CTCGCCGCCT TCGGAAACTG CAGCGGAGGG AGAAGAAAGG GAAGTGTGTG 1740 AAGCCCTGAG GGCCTCGTGC CCCACGCGGG TCCCGGCCCC ACTGCACACG CAGACCATGC 1800 CCAGAGACTC TGTACATACA TATCGTGTGA ACGGACTCTT CTGTCTATAG TGTATATTTT 1860 GGCAACGGTT CCCCTTTTTG TGTGCGTGTG CACGCGTGGG TGTGTGCACG TGTGTGTGCG 1920 TGTGTGTGTG TGTGTGTGTG TGTGTCTCCT CTCAGTGTGT ATTAAAAATA AGGCGGTAAT 1980 GACAAACCTT TAATGAGGAG CAAAGCAGAG GGGGTCCTGT GGGTGCCTGC TGCCTGAAGG 2040 AGCTTGAGGG GCTGGTTTCT TGCTCCGGGC GTGCTGTTCC TCACCCTTCT GTCCTACTCT 2100 CTCTTTCCCC TTGAGCAAAA CCTTCTGCCC AGTGCTGCTG TCTGAGCTCG CGGCTCTCCC 2160 TGCTGCAGAG CCCGGTCCCT CTCACGTGCT GCACATGTGC TGCTCTCAGC TCTCTGTGCC 2220 CCTTTTCTTG TGCAGCAGAG ACGGGAGGTC GGTTTCCTCC-ATCCCGCTGC ACACACGGAC 2280 CGGCTGGGTG GAGACCATCC AGCGCTGCAG GACCGGCCCC AGGAGCTCCG CTGGGAGAAC 2340 CAAGTGACCT TTCTCCAGGC CTGATCCTGC AGGACCTCAG CTTTACATGG ACTGGTCGTG 2400 CCGCCCAGGG GCAGGGCCCA TGGAAGTCTT GGGGACAGCC AGGGCTGTTG GCCACCACCC 2460 CACAGAGCTG TTCTGAGCAG GGCGCAGGGG TCTGCCTGTC CTGGTGCGTG GTCCAGGTGA 2520 CCCAWCAGGA AAGACCTGCA GATACCCATA TTCTCCTCTC GTGCCAGCTC TGCATGCTGC 2580 TGTGACCTTG GCCGTGCCAG AGGTGCAGAG GCAGAGGTGG CAGGAAGAGA GGAGAGCTTT 2640 CGCTGACCAA CCTCCAGTCT TTCATTTCTT CTKCATACTG TATTAGTCTC CAGTTCAAAC 2700 AGACATCAGT TTCTTTCCAC GTTGAGGTTA TAGTGGTCTC GAYGTAATAA ACATGAATGG 2760 AAATAATAAA AAAAAAAAAA AAA 2783 (2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 581 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4: Leu Arg Leu Leu Leu Thr Thr Ser Val Leu Arg Leu Ala Arg Ala Ala 1 5 10 15 Asn Pro Phe Val Ala Gin Gin Thr Pro Pro Asp Pro Cys Tyr Asp Glu 20 25 30 Ser Gly Ala Pro Pro Arg Cys He Pro Glu Phe Val Asn Ala Ala Phe 35 40 45 Gly Lys Glu Val Gin Ala Ser Ser Thr Cys Gly Lys Pro Pro Thr Arg 50 55 60 His Cys Asp Ala Ser Asp Pro Arg Arg Ala His Pro Pro Ala Tyr Leu 65 70 75 80 Thr Asp Leu Asn Thr Ala Ala Asn Met Thr Cys Trp Arg Ser Glu Thr 85 90 95 Leu His His Leu Pro His Asn Val Thr Leu Thr Leu Ser Leu Gly Lys 100 105 110 Lys Phe Glu Val Val Tyr Val Ser Leu Gin Phe Cys Ser Pro Arg Pro 115 120 125 Glu Ser Thr Ala He Phe Lys Ser Met Asp Tyr Gly Lys Thr Trp Val 130 135 140 Pro Tyr Gin Tyr Tyr Ser Ser Gin Cys Arg Lys He Tyr Gly Lys Pro 145 150 155 160 Ser Lys Ala Thr Val Thr Lys Gin Asn Glu Gin Glu Ala Leu Cys Thr 165 170 175 Asp Gly Leu Thr Asp Leu Tyr Pro Leu Thr Gly Gly Leu He Ala Phe 180 185 190 Ser Thr Leu Asp Gly Arg Pro Ser Ala Gin Asp Phe Asp Ser Ser Pro 195 200 205 Val Leu Gin Asp Trp Val Thr Ala Thr Asp He Arg Val Val Phe Ser 210 215 220 Arg Pro His Leu Phe Arg Glu Leu Gly Gly Arg Glu Ala Gly Glu Glu 225 230 235 240 Asp Gly Gly Ala Gly Ala Thr Pro Tyr Tyr Tyr Ser Val Gly Glu Leu 245 250 255 Gin Val Gly Gly Arg Cys Lys Cys Asn Gly His Ala Ser Arg Cys Val 260 265 270 Lys Asp Lys Glu Gin Lys Leu Val Cys Asp Cys Lys His Asn Thr Glu 275 280 285 Gly Pro Glu Cys Asp Arg Cys Lys Pro Phe His Tyr Asp Arg Pro Trp 290 295 300 Gin Arg Ala Ser Ala Arg Glu Ala Asn Glu Cys Leu Ala Cys Asn Cys 305 310 315 320 Asn Leu His Ala Arg Arg Cys Arg Phe Asn Met Glu Leu Tyr Lys Leu 325 330 335 Ser Gly Arg Lys Ser Gly Gly Val Cys Leu Asn Cys Arg His Asn Thr 340 345 350 Ala Gly Arg His Cys His Tyr Cys Lys Glu Gly Phe Tyr Arg Asp Leu 355 360 365 Ser Lys Ser He Thr Asp Arg Lys Ala Cys Lys Ala Cys Asp Cys His 370 375 380 Pro Val Gly Ala Ala Gly Lys Thr Cys Asn Gin Thr Thr Gly Gin Cys 385 390 395 400 Pro Cys Lys Asp Gly Val Thr Gly Leu Thr Cys Asn Arg Cys Ala Lys 405 410 415 Gly Phe Gin Gin Ser Arg Ser Pro Val Ala Pro Cys He Lys He Pro 420 425 430 Ala He Asn Pro Thr Ser Leu Val Thr Ser Thr Glu Ala Pro Ala Asp 435 440 445 Cys Asp Ser Tyr Cys Lys Pro Ala Lys Gly Asn Tyr Lys He Asn Met 450 455 460 Lys Lys Tyr Cys Lys Lys Asp Tyr Val Val Gin Val Asn He Leu Glu 465 470 475 480 Met Glu Thr Val Ala Asn Trp Ala Lys Phe Thr He Asn He Leu Ser 485 490 495 Val Tyr Lys Cys Arg Asp Glu Arg Val Lys Arg Gly Asp Asn Phe Leu 500 505 510 Trp He His Leu Lys Asp Leu Ser Cys Lys Cys Pro Lys He Gin He 515 520 525 Ser Lys Lys Tyr Leu Val Met Gly He Ser Glu Asn Ser Thr Asp Arg 530 535 540 Pro Gly Leu Met Ala Asp Lys Asn Ser Leu Val He Gin Trp Arg Asp 545 550 555 560 Ala Trp Thr Arg Arg Leu Arg Lys Leu Gin Arg Arg Glu Lys Lys Gly 565 570 575 Lys Cys Val Lys Pro 580 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 2166 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: TGTATGTTGT GTGRRTTGTG ANNNNATAAC AATTTCACAC AGGAAACAGC NNNNNNNNNN 60 NNNNNNGCTA CTGCGTGGTG AGCGAGCGTG GTGAAGAGCG CGTGCGCTCC TGTCACCTCT 120 GCAACTCTTC GGATCCCAAG AAAGCGCACC CGCCCGCCTT CCTCACCGAC CTCAATAACC 180 CGCACAACCT GACGTGCTGG CAGTCCGAGA ACTACCTGCA GTTCCCGCAC AACGTGACGC 240 TCACTCTGTC GCTCGGCAAG AAGTTTGAGG TGACCTATGT GAGCCTGCAA TTCTGCTCGC 300 CGCGGCCAGA GTCCATGGCC ATCTACAAGT CCATGGACTA CGGGCGCACG TGGGTGCCCT 360 TCCAGTTCTA TTCCACGCAG TGCCGCAAAA TGTACAACCG GCCGCACCGC GCGCCTATCA 420 CCAAACAGAA CGAGCAGGAG GCCGTGTGCA CCGACTCGCA CACCGACATG CGCCCGCTCT 480 CTGGCGGGCT GATCGCTTTC AGCACGCTGG ACGGGCGGCC CTCGGCGCAC GACTTCGACA 540 ACTCGCCGGT GCTGCAGGAC TGGGTCACGG CCACCGACAT CCGCGTGGCT TTCAGCCGCC 600 TGCACACGTT CGGCGACGAG AACGAAGACG ACTCGGAGCT GGCGCGCGAC TCCTATTACT 660 ATGCAGTGTC TGACCTGCAG GTTGGCGGCC GCTGCAAGTG CAACGGCCAC GCGGCGCGTT 720 GCGTGCGCGA CCGAGACGAC AGTCTGGTGT GTGACTGTAG GCACAACACG GCCGGCCCTG 780 AATGCGACCG TTGCAAGCCC TTCCACTACG ACCGGCCCTG GCAGCGCGCC ACGGCCCGCG 840 AGGCCAACGA GTGCGTGGCC TGCAACTGCA ACCTCCATGC TCGGCGCTGC AGATTCAACA 900 TGGAGCTCTA TAAGCTATCA GGGCGCAAGA GCGGGGGAGT STGTCTCAAC TGCCNNNACA 960 ACACTCNNNG CCGCCACTGC CACTACTGNN AAGGAGGGNN NCTTCTACCG AGACATGGGC 1020 AAGCCTATCA CCCACCGGAA GGCTTGCAAA GCCTGTGATT GCCACCCAGT GGGTGCTGCT 1080 GGCAAGACCT GCAATCAAAC CACTGGCCAA TGTCCCTGCA AGGACGGCGT GACGGGCATC 1140 ACCTGCAACC GATGTGCCAA AGGCTACCAG CAGAGCCGTT CCCCCATCGC CCCTTGCATC 1200 AAGATTCCTG TGGCGCCGCC CACCACTGCA GCCAGCAGCN GTGGAGGAAC NNNNGGAAGA 1260 CTGTGATTCC TATTGCAAGG CCTCCAAAGG CAAGCTGAAG ATGAACATGA AGAAATACTG 1320 CAGGAAGGAC TATGCTGTCC AGATCCACAT CCTGAAGGCC GACAAAGCAG GGGACTGGTG 1380 GAAGTTCACC GTGAACATCA TCTCCGTGTA CAAGCAGGGC ACAAGTCGTA TTCGCCGTGG 1440 TGACCAGAGT TTGTGGATCC GCTCACGAGA CATCGCCTGY AAGTGTCCCA AAATCAAGCC 1500 CCTCAAGAAG TACTTGCTGT TGGGTAATGC CNGAGGACTC ACCTGACCAG AGTGGCATCG 1560 TGGCAGACAA GAGCAGCCTG GTGATCCAGT GGCGGGACAC ATGGGCACGG CGGCTGCGCA 1620 AGTTCCAGCA ACGGGAGAAG AAGGGCAAGT GCAAGAAGGC CTAGCGCGGA GGTGGCGCGG 1680 GCTCCAGGAG GGCGGGCAGG GCGCTGGCAA AGGCTGGCAG CCTTGGACTT GGCCGTCAGG 1740 GGNNTTTTTK GGAGGGTGGG NNNCGGGGCG AAGTCGAAGT GGCGGGGCCC TCAGCCGTCC 1800 GCCCCAGCCC CWCCCTCACA CCCCTGGCTG CGCTCTTATG GCGCATGGGC AGAAAGCNCC 1860 CTGTATTGAC AGGCCAGGCC CTGGANAAAT GAGGACAAGA CATAGCTACC TCACGGCGCT 1920 CCTTCCAGAA CAGAGATGCG CTTCCCTAGG GCTAGGTGGG GGTCGCNNGT GGAGGGGTTA 1980 GGGAGGTCCT GAGAGGCGGG AACAGAATGG CACAGTGGTC TACAGTCGCT GTGTTTGATG 2040 GTTATTGAAG GGGGATGTAA GAACTGTGAA TTTTTGGGCC TGCNNCCTGG GCCAGGGGNA 2100 ACCAATCCAC CACCAGACAC TAGTCACGCC CCCCTCCTTT CTCCATCACC CGCTGTCTAG 2160 GAATTC 2166 (2) INFORMATION FOR SEQ ID NO:6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 529 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6: Tyr Cys Val Val Ser Glu Arg Gly Glu Glu Arg Val Arg Ser Cys His 1 5 10 15 Leu Cys Asn Ser Ser Asp Pro Lys Lys Ala His Pro Pro Ala Phe Leu 20 25 30 Thr Asp Leu Asn Asn Pro His Asn Leu Thr Cys Trp Gin Ser Glu Asn 35 40 45 Tyr Leu Gin Phe Pro His Asn Val Thr Leu Thr Leu Ser Leu Gly Lys 50 55 60 Lys Phe Glu Val Thr Tyr Val Ser Leu Gin Phe Cys Ser Pro Arg Pro 65 70 75 80 Glu Ser Met Ala He Tyr Lys Ser Met Asp Tyr Gly Arg Thr Trp Val 85 90 95 Pro Phe Gin Phe Tyr Ser Thr Gin Cys Arg Lys Met Tyr Asn Arg Pro 100 105 110 His Arg Ala Pro He Thr Lys Gin Asn Glu Gin Glu Ala Val Cys Thr 115 120 125 Asp Ser His Thr Asp Met Arg Pro Leu Ser Gly Gly Leu He Ala Phe 130 135 140 Ser Thr Leu Asp Gly Arg Pro Ser Ala His Asp Phe Asp Asn Ser Pro 145 150 155 160 Val Leu Gin Asp Trp Val Thr Ala Thr Asp He Arg Val Ala Phe Ser 165 170 175 Arg Leu His Thr Phe Gly Asp Glu Asn Glu Asp Asp Ser Glu Leu Ala 180 185 190 Arg Asp Ser Tyr Tyr Tyr Ala Val Ser Asp Leu Gin Val Gly Gly Arg 195 200 205 Cys Lys Cys Asn Gly His Ala Ala Arg Cys Val Arg Asp Arg Asp Asp 210 215 220 Ser Leu Val Cys Asp Cys Lys His Asn Thr Ala Gly Pro Glu Cys Asp 225 230 235 240 Arg Cys Lys Pro Phe His Tyr Asp Arg Pro Trp Gin Arg Ala Thr Ala 245 250 255 Arg Glu Ala Asn Glu Cys Val Ala Cys Asn Cys Asn Leu His Ala Arg 260 265 270 Arg Cys Arg Phe Asn Met Glu Leu Tyr Lys Leu Ser Gly Arg Lys Ser 275 280 285 Gly Gly Val Cys Leu Asn Cys Xaa Xaa Asn Thr Xaa Xaa Arg His Cys 290 295 300 His Tyr Xaa Xaa Gly Gly Xaa Leu Leu Pro Arg His Gly Lys Pro He 305 310 315 320 Thr His Arg Lys Ala Cys Lys Ala Cys Asp Cys His Pro Val Gly Ala 325 330 335 Ala Gly Lys Thr Cys Asn Gin Thr Thr Gly Gin Cys Pro Cys Lys Asp 340 345 350 Gly Val Thr Gly He Thr Cys Asn Arg Cys Ala Lys Gly Tyr Gin Gin 355 360 365 Ser Arg Ser Pro He Ala Pro Cys He Lys He Pro Val Arg Arg Pro 370 375 380 Thr Ala Ala Ser Xaa Val Glu Glu Xaa Xaa Glu Asp Cys Asp Ser Tyr 385 390 395 400 Cys Lys Ala Ser Lys Gly Lys Leu Lys Met Asn Met Lys Lys Tyr Cyε 405 410 415 Arg Lys Asp Tyr Ala Val Gin He His He Leu Lys Ala Asp Lys Ala 420 425 430 Gly Asp Trp Trp Lys Phe Thr Val Asn He He Ser Val Tyr Lys Gin 435 440 445 Gly Thr Ser Arg He Arg Arg Gly Asp Gin Ser Leu Trp He Arg Ser 450 455 460 Arg Asp He Ala Cys Lys Cys Pro Lys He Lys Pro Leu Lys Lys Tyr 465 470 475 480 Leu Leu Leu Gly Asn Ala Xaa Asp Ser Pro Asp Gin Ser Gly He Val 485 490 495 Ala Asp Lys Ser Ser Leu Val He Gin Trp Arg Asp Thr Trp Ala Arg 500 505 510 Arg Leu Arg Lys Phe Gin Gin Arg Glu Lys Lys Gly Lys Cys Lys Lys 515 520 525 Ala

Claims: WHAT IS CLAIMED IS: 1. An isolated peptide comprising a unique portion of SEQUENCE ID NO:2, 4 or 6, wherein said peptide is capable of selectively increasing spinal axon outgrowth or directing spinal axon ourgrowth orientation. 2. A peptide according to claim 1, wherein said peptide comprises a unique portion of an EGF-like repeat of netrin 1 or netrin2. 3. An isolated antibody that selectively binds a peptide according to claim 1. 4. A nucleic acid encoding a peptide according to claim 1 joined directly to a nucleotide not naturally joined to said nucleic acid. 5. A cell comprising a nucleic acid according to claim 5. 6. A transgenic nonhuman animal comprising a nucleic acid according to claim 4 wherein said nucleic acid is xenogeneic to said animal. 7. A process for the production of a peptide comprising a unique portion of a neural axon outgrowth promoting protein comprising culturing the cell of Claim 5 under conditions suitable for the expression of said peptide, and recovering said peptide. 8. A method of identifying a pharmacological agent useful in the diagnosis or treatment of disease associated with the binding of a neural axon outgrowth promoting protein to a receptor, said method comprising the steps of: contacting a panel of prospective agents with a peptide according to claim l; measuring the binding of a plurality of said prospective agents to said peptide; identifying from said plurality a pharmacological agent which selectively binds said peptide; wherein said pharmacological agent is useful in the diagnosis or treatment of disease associated with the binding of a neural axon outgrowth promoting protein to a receptor. 9. A method of diagnosing a patient for a predisposition to neurological disease associated with a genetic locus, said method comprising the steps of: isolating somatic cells from a patient; isolating genomic DNA from said somatic cells; contacting said genomic DNA with a probe comprising a DNA sequence encoding a peptide according to claim 1 under conditions wherein said probe is capable of selectively hybridizing with homologous DNA; identifying a region of said genomic DNA which hybridizes with said probe; wherein the presence, absence or sequence of said region correlates with a predisposition to a neurological disease. 10. A method of treating a patient with neurological injury or disease, said method comprising the steps of: administering to a patient a therapeutically effective dosage of a pharmaceutical composition comprising a pharmaceutically acceptable carrier and a peptide according to claim 1; wherein said peptide modulates axon outgrowth in said patient.

Inventors: DODD JANE, JESSELL THOMAS, KENNEDY TIMOTHY, PLACZEK MARYSIA, SERAFINI TITO, TESSIER-LAVIGNE MARC, DODD, JANE, JESSELL, THOMAS, KENNEDY, TIMOTHY, PLACZEK, MARYSIA, SERAFINI, TITO, TESSIER-LAVIGNE, MARC
Applicants: UNIV CALIFORNIA, UNIV COLUMBIA, COLUMBIA UNIVERSITY, THE REGENTS OF THE UNIVERSITY OF CALIFORNIA
Application year: 1994
Main classification: C12N15
IPC codes: A01K67, A61K38, A61P25, C07K14, C12N5, C12N15, C12P21, C12R1, G01N33